Surface Ia Expression Research Articles

Peritoneal and Splenic Macrophage Functions in the Tumor-Bearing Host

In the tumor-bearing host, depression of cell-mediated immunity has been well-demonstrated, but little is known about alterations in macrophage functions. We hypothesized that the presence of a tumor may cause functional suppression of peritoneal macrophage and splenic macrophage functions, perhaps due to prostaglandin-E 2 (PGE 2) and nitric oxide. C57 BL/6 mice ( n = 18) were injected subcutaneously with Lewis lung carcinoma 3 tumor. Control mice ( n = 18) received no tumor and were pair-fed to intake of the tumor group. On Day 21, peritoneal and splenic macrophages were harvested. Cell surface Ia expression, cytotoxicity against P815 target cells, Candida albicans killing, and production of PGE 2, nitric oxide, and superoxide were measured. Mean Ia expression was decreased in tumor animals for both peritoneal and splenic macrophages. In tumor animals PGE 2 production significantly increased in both peritoneal and splenic macrophages. Superoxide production significantly decreased in peritoneal macrophages but significantly increased in splenic macrophages. Nitric oxide production was also significantly depressed in tumor-bearing host peritoneal macrophages. C. albicans killing was significantly depressed in tumor animals' peritoneal macrophages but showed little change in splenic macrophages. In tumor animals cytotoxicity was significantly decreased in peritoneal macrophages but significantly increased in splenic macrophages. In the tumor-bearing host, peritoneal macrophages have significantly decreased accessory and effector functions. Splenic macrophages demonstrate decreased accessory but enhanced effector functions. PGE 2, superoxide, and nitric oxide appear to be important mechanisms of altered macrophage function in the tumor-bearing host; modifying their cellular production may enhance host defense.

Modulation of airway intraepithelial dendritic cells following exposure to steroids.

Recent studies from our laboratory have identified a network of constitutively class II major histocompatibility complex (MHC) (Ia)-bearing dendritic cells (DC) within the epithelium of the conducting airways of laboratory animal species and in humans. These studies have also demonstrated that the density of the DC network increases within the airway epithelium in response to inflammatory challenge. In the present report, we demonstrate that exposure of adult rats to inhaled steroids leads to a rapid but readily reversible decrease both in the number of airway intraepithelial DC, and in their surface Ia expression. Similar changes are also seen in response to high doses of systemic dexamethasone. In addition, we demonstrate that steroid inhalation reduces the rate of postnatal expansion of the airway intraepithelial DC network in rat pups, and prevents the rapid expansion of the DC network in adults which occurs during the acute inflammatory response following inhalation of microbial stimuli.

Splenic macrophage activation and functions in amyloid enhancing factor-induced secondary amyloidosis Study of phagocytosis, killing, respiratory burst, and MHC class II surface expression

Secondary amyloidosis is a systemic disease characterized by the extracellular tissue deposition of insoluble fibrillar amyloid A protein. Aberrant metabolism of serum amyloid A protein by reticuloendothelial cells is thought to result in the accumulation of fibrils within the tissue. Treatment of mice with amyloid-enhancing factor (AEF) in conjunction with an inflammatory stimulus (i.e., AgNO3) induced amyloid deposition within 48-72 h. The activation state of a macrophage largely defines its enzymatic capabilities. In the studies reported here, we examined the effect of AEF on spleen macrophage activation using both functional and phenotypic assays. We found that while AEF in the presence or absence of AgNO3 has no apparent effect on the ability of spleen and liver macrophages to phagocytose or kill Listeria monocytogenes, it appears to block enhanced respiratory burst function (as measured by O2- production) observed with AgNO3 alone. AEF therefore seems capable of inhibiting certain macrophage activation-associated functions while not affecting others. Our activation phenotype studies, using surface Ia expression, reveal that AEF blocks the increase in number of splenic macrophages expressing Ia seen with AgNO3 alone. Treatment with interferon-gamma was found to restore decreased Ia expression in animals given AEF+AgNO3 but did not prevent amyloid A fibril deposition.

Suppression of Ia antigen expression on gamma interferon treated macrophages infected with Ehrlichia risticii

Ehrlichia risticii is an obligate intracellular bacterium of monocytes/macrophages. In this report, using immunofluorescence staining, flow cytometry, and Kolmogorov-Smirnov analysis of histograms, the response of P338D 1 and peritoneal macrophages stimulated with recombinant murine interferon-γ (rIFN-γ) was examined for the expression of major histocompatibility complex Class II gene product (Ia) and effect of E. risticii infection on induction of Ia surface expression. Maximal expression of Ia by sham-infected P388D 1 cells was observed 2 days post rIFN-γ addition followed by a progressive decline. These stimulatory effects of rIFN-γ were dose dependent. Relative to sham-infected P388D 1 cells, the induction of Ia by rIFN-γ (200 U ml −1) on E. risticii-infected P388D 1 cells was significantly suppressed at each time point tested through Day 5 with maximal suppression of 88% occurring on Day 2. Similarly, the induction of Ia by rIFN-γ on E. risticii-infected peritoneal macrophages was significantly suppressed by 77% (fluorescent microscopy) when compared to sham-infected peritoneal macrophages. The higher dose of rIFN-γ (2000 U ml −1) failed to restore Ia surface expression by E. risticii-infected P388D 1 cells. The suppression of Ia on P388D 1 cells in response to RIFN-γ was not related to the degree of infection of these cells by E. risticii. A soluble inhibitor substance was not demonstrable in the supernatant from E. risticii-infected cells, nor were inhibitor levels of prostaglandin E 2 levels found in the supernatant. Suppression of surface Ia expression on the macrophage suggests a mechanism whereby I. risticii may evade T-lymphocyte recognition, hinder antigen-specific T-lymphocyte activation, and promote their own survival.

Kupffer Cell Engraftment Across the Major Histocompatibility Barrier in Mice

The source of population renewal for Kupffer cells (KC), the major antigen-presenting cells of the liver, remains controversial. Using a well-described murine bone marrow transplantation (BMT) model in which the donor and recipient are disparate at the major histocompatibility complex (MHC), we have studied (a) the source of KC renewal by genotypic analysis, cell surface (class II or Ia) antigens, and immune function assays; (b) the level of KC Ia expression post-BMT in transplant recipients; and (c) the capacity of newly repopulating KC to present antigen to an Ia-restricted T cell clone of donor Ia type. Kupffer cell engraftment, as assessed by each of these three methods, was noted to be predominantly of donor marrow origin by day 21 post-BMT. Cell surface Ia expression was comparable to that of nontransplanted controls of the same strain as donor mice. Within 7 days post-BMT, KC were mature antigen-presenting cells. We conclude that KC rapidly repopulate the liver from donor bone marrow post-BMT, and these macrophages are able to interact with T lymphocytes in an immunocompetent manner.

The induction of murine B cell Ia by IgE-antigen complexes is dependent on protein synthesis and preceded by class II mRNA accumulation

Complexes of murine monoclonal anti-DNP IgE and DNP-OVA interact with murine B cells` to stimulate expression of cell surface Ia antigens. Enhanced membrane expression of class II MHC antigens was accompanied by a threefold increase of I-A and I-E transcripts, as measured by Northern blot. Peak accumulation of Ia mRNA were detected after 6 hr of incubation with IgE-antigen complexes and returned to control levels after 12 hr of incubation. Hence, induction of Ia mRNA by IgE-antigen complexes was compatible with cell surface Ia expression, both quantitatively and with regard to the time frame. The Ia-inductive effects of both IL-4 and IgE-antigen complexes were inhibited by cycloheximide and actinomycin-D. However, whereas actinomycin-D and cycloheximide blocked IL-4 induction of FcϵRII expression, inhibition of transcription or protein synthesis did not abrogate the increased expression of FcϵR associated with IgE-antigen complexes. These results suggest that the IgE-antigen-induction of B cell Ia expression follows from activation of transcription and de novo synthesis of Ia antigens.

Interferon-gamma Increases Alveolar Macrophage Ia Antigen Expression Despite Oral Administration of Dexamethasone to Rats

Corticosteroids have multiple effects on immune and inflammatory responses and decrease host resistance to a broad range of microorganisms. Resident tissue macrophages have been proposed as a target for the immunosuppressive effects of corticosteroids and are important in host defense against infections. During infection-induced immune responses, macrophages are activated after exposure to interferon-gamma (IFN-gamma), and class II major histocompatibility (Ia) antigens on their surface are increased. We investigated the effect of orally administered corticosteroids on alveolar macrophages, the resident macrophages of the lung parenchyma. We hypothesized that corticosteroids would inhibit the activation of alveolar macrophages and measured induction by IFN-gamma of Ia antigens as a marker of cell activation. Alveolar macrophages from normal and corticosteroid-treated rats were exposed to recombinant murine IFN-gamma (rMuIFN-gamma) in vitro and assayed for Ia transcription and surface Ia expression. Ia mRNA accumulation was induced in alveolar macrophages from normal and corticosteroid-treated rats after exposure in vitro to rMuIFN-gamma. Furthermore, rMuIFN-gamma increased surface expression of Ia proteins on alveolar macrophages from corticosteroid-treated rats, although to a lesser extent than on cells from control rats. Finally, surface Ia expression could also be increased in vivo by exposure of corticosteroid-treated rats to an aerosol containing rMuIFN-gamma. These results demonstrate that administration of oral corticosteroids, while establishing a state of immunosuppression in rats, does not abolish responsiveness of rat alveolar macrophages to rMuIFN-gamma. We speculate that IFN-gamma-induced augmentation of phagocytic cell function may constitute an important therapeutic modality to treat complications of immunodeficiency.

A role for endogenous retroviral sequences in the regulation of lymphocyte activation.

The genomes of most vertebrates contain numerous retroviral sequences, the great majority of which are non-infectious. These endogenous retroviral sequences are transcribed and translated in many host tissues, and are induced by mitogens. The function, if any, of endogenous retroviruses has been unclear. The transmembrane envelope proteins of some infectious type C retroviruses suppress lymphocyte activation, but it is unknown whether any endogenous type C retroviruses share this suppressive activity. To study the possible effects of murine endogenous retroviral expression, specific antisense oligonucleotides were synthesized complementary to type C retroviral sequences, and were cultured with murine spleen cells. If any of these endogenous retroviruses are suppressing lymphocyte activation, then inhibiting such endogenous retroviral-mediated suppression with antisense might result in lymphocyte stimulation. Three classes of endogenous type C retroviral sequences may be distinguished by antisense oligonucleotides (based on their homology to infectious retroviruses): ecotropic, xenotropic, and mink cell focus-forming (MCF). Antisense oligonucleotides to endogenous MCF envelope gene (env) initiation regions caused: i) doubling or tripling of spleen cell RNA synthesis, and ii) marked increases in lymphocyte surface Ia and Ig expression relative to control oligonucleotides. Antisense oligos to xenotropic or ecotropic env sequences or to endogenous MCF non-envelope sequences had no effect. These data suggest that endogenous MCF sequences exert an inhibitory influence on the murine immune system. Because endogenous MCF expression is inducible by immune stimuli, such expression could constitute an inhibitory feedback circuit that participates in the regulation of immune homeostasis.

Lymph node macrophage heterogeneity: the phenotypic and functional characterization of two distinct populations of macrophages from rat lymph node

The isolation and characterization of lymph node macrophages (M phi) has shown a hitherto unknown heterogeneity. Two types of M phi were distinguished by morphology, monoclonal antibody staining and functional assays. The type I M phi failed to express surface Ia even when activated, a characteristic which has only previously been reported for splenic marginal zone M phi; despite studies suggesting an antigen presentation role for the M phi, the failure to express surface Ia would seem to eliminate an interaction with T helper cells for the type I M phi in the lymph node. In contrast, the type I M phi, other characteristics of clustering with activated B cells in vitro, the colocalization of the type I M phi and activated B cells in situ, the specific uptake of thymus-independent type 2 antigens and the failure to undergo respiratory burst activity all suggest a M phi-B cell interaction, possibly of a trophic nature. The defective microbicidal activity of the type I M phi may have been compensated for by the type II M phi, which expresses both strong respiratory burst activity and surface Ia expression when freshly isolated. However, unlike the inflammatory M phi the activated phenotype of the type II M phi did not appear to be interferon-gamma dependent because type II M phi could also be isolated from nude rat lymph nodes.

Lymphokine regulation of surface Ia expression on rat B cells

Class II major histocompatibility antigens (Ia) play a major role in regulating T-B cell interactions; therefore, regulation of the amount of Ia on B cells may be an important point of control in the immune response. Mitogens in human and murine systems have been reported to increase Ia expression on B cells, and in the mouse the lymphokine BSF-1 (IL-4) markedly enhances Ia expression. This report describes studies of lymphokine and mitogen regulation of class II expression on rat B cells. Mitogens known to activate resting B cells, such as DxS/LPS, anti-IgM, STM, and Con A, induced increases in Ia expression. Highly purified murine IL-4 was found to have no Ia-enhancing activity on rat B cells, although the same preparation increased Ia expression eightfold on murine B cells. This confirms other recent reports that IL-4 is a species-specific lymphokine and will not cross even narrow phylogenetic barriers. Rat B cells were not refractory to lymphokine-induced enhancement of Ia expression, since lymphokine(s) contained in a Con A-induced supernatant enhanced Ia expression. Furthermore, murine IL-5-containing B151-CFS was able to markedly increase Ia expression on resting rat and mouse B cells. This activity was not lost after heat inactivation of B151-TRF2, indicating that B151-TRF1 (IL-5-like activity) was probably responsible for the increase in Ia expression. These results suggest Ia expression on rat B cells, like human and murine B cells, is an early activation event which is regulated by signals which act on resting B cells. Furthermore, while IL-4 is important in Ia regulation, it is not the only lymphokine involved, since the IL-4-free, B151-K12 supernatant was able to enhance Ia expression on resting rat and mouse B cells.

Ly1+ PRO-B lymphocyte clones. Phenotype, growth requirements and differentiation in vitro and in vivo.

Several clones obtained from the bone marrow of a BALB/c mouse were found to contain the heavy and light chain Ig genes in the germline configuration, to express Ly1 and to carry the B cell lineage markers B-220, Lyb8 and BP-1; these clones are Pgp-1+, LFA-1+, J11d+, Mac-1+ and Thy1-, Lyt2-, L3T4-, GM1.2- and Ia-. Three clones analyzed in detail (Lyd9, LyH7 and Lyb9) have receptors for interleukin (IL) 2 and IL3 as assessed with the 7D4 and CC11 monoclonal antibodies respectively. They grow in rIL3 but not in rIL2 or rIL1; both rIL4 and rIL5 also promote their proliferation, albeit to a much lesser extent than rIL3. None of the interleukins tested alone or in various combinations promoted the clones to differentiate in vitro along the B cell pathway. Treatment with 5-Azacytidine (5-Aza) induced cell surface Ia expression but not rearrangement or expression of Ig genes. However, 5-Aza-treated Lyd9, LyH7 and Lyb9 cells co-cultured with X-ray irradiated accessory cells and LPS gave rise to Ly1+, IgM+ B lymphocytes (range 14-51%) including mu + kappa + (78-93%), and mu + lambda + (9-25%) B lymphocytes. In vivo, the Lyd9, LyH7 and Lyb9 clones gave rise to IgM+ B lymphocytes (8.5-17%) including mu + kappa +, and mu + lambda +, but not to Lyt2+ or L3T4+ T lymphocytes after 4-6 weeks of transfer into Scid mice. Our results indicate that Ly1+ IgM+ cells comprise a subpopulation of B lymphocytes that is derived from IL3-responsive Ly1+ PRO-B lymphocytes.

Interleukin 4 enhances the ability of antigen-specific B cells to form conjugates with T cells.

T cell-B cell conjugates are formed when trinitrophenyl-specific B cells are exposed to trinitrophenyl-ovalbumin and ovalbumin-specific T hybridoma cells. The proportion of conjugates was increased two- to threefold when antigen-pulsed trinitrophenyl-specific B cells, but not T cells, were pre-exposed to interleukin 4. Antigen-specific B cells pretreated with antigen and interleukin 4 and cultured in the presence of specific T helper cells also produced a larger proportion of antibody-secreting cells as compared to cells pretreated with antigen alone. The interleukin 4-induced enhancement of T/B conjugate formation occurred over a wide range of antigen concentrations, was dependent on the concentration of interleukin 4, and was inhibited by the monoclonal anti-interleukin 4 antibody, 11B11. The importance of Ia antigens in the enhancement of conjugate formation and generation of antibody-secreting cells is suggested by a) the fact that the interleukin 4-mediated increase in the density of Ia antigens on the antigen-specific B cells correlated with their enhanced ability to form T/B conjugates, b) the kinetics of the interleukin 4-mediated increase in conjugate formation and surface Ia expression were similar, c) 10- to 20-fold higher concentrations of anti-I-A antibody were required to inhibit T/B conjugate formation by 50% with interleukin 4-treated antigen-specific B cells compared with untreated antigen-specific B cells, and d) interferon-gamma, which inhibits the interleukin 4-mediated increase in Ia antigens, inhibited the interleukin 4-induced enhancement of T/B conjugate formation. These results indicate that the interleukin 4-induced increase in the expression of Ia antigens on B cells plays an important role in the enhancement of T/B cell interactions and the subsequent differentiation of antigen-specific B cells into antibody-secreting cells.

Suppressed expression of surface Ia on macrophages by lipopolysaccharide: evidence for regulation at the level of accumulation of mRNA.

The surface expression of class II major histocompatibility molecules (immune associated or Ia antigens) is an acquired property of macrophages, essential to their ability to interact effectively with T lymphocytes. Surface expression of Ia is induced by stimulants such as interferon-gamma and is suppressed by agents such as lipopolysaccharide (LPS). Recent studies on several cultured cell lines indicate that interferon-gamma can heighten cellular levels of mRNA encoding Ia, and the level of such mRNA may represent an important regulatory focus for controlling expression of surface Ia. Murine peritoneal macrophages were treated with interferon-gamma and/or LPS and expression of Ia mRNA determined by Northern blot analysis with a probe specific for the murine beta-chain of I-A. mRNA specific for I-A beta was not detectable in explanted macrophages obtained from sites of sterile inflammation but was induced by treatment of purified recombinant interferon-gamma. This effect was dose dependent and was optimal by 24 hr after stimulation. Ia-specific mRNA preceded the surface expression of Ia as monitored by a radioimmunoassay using a monoclonal antibody specific for I-A beta. When a physiologic dose of LPS was added concomitantly with the interferon-gamma, the time course of induction if Ia-specific mRNA was not altered, but the amount of such mRNA detected was suppressed 40 to 80%. This effect was dependent on the dose of LPS, and the levels of mRNA correlated closely with subsequent surface expression of Ia. The ability of LPS to suppress both mRNA and cell surface Ia expression required that the suppressive agent be added within 12 hr of the inducing stimulus. This is the time frame during which accumulation of mRNA occurs. Thus the data demonstrates that accumulation of specific mRNA is a major regulatory focus governing expression of Ia both by interferon-gamma and LPS.

Activation of specific T cell lines by the antigens avidin and myelin basic protein in the absence of antigen‐presenting cells

We have investigated the specific activation by soluble antigen of rat or mouse long-term T helper cell lines using antigen-presenting cell (APC)-free culture conditions. Some T cell lines specific for avidin or myelin basic protein responded to native antigen in the absence of added APC. Responses in the absence of APC were substantial and specific although, as would be expected, lower than in the presence of APC. Proliferation could not be inhibited by culture with anti-Ia antibodies and the ability of lines to respond to antigen in the absence of APC did not correlate with the endogeneous surface Ia expression of the lines. Furthermore, irradiated T cells were unable to act as presenting cells for lines cells of the same or a different specificity. This suggests that the T cells did not present antigen to each other, and demonstrates, along with other data shown, that activation cannot be attributed to undetected APC remaining in the cultures. Anti-avidin T cell lines differed markedly in their ability to respond to avidin in the absence of added APC.S2, an anti-avidin line of H-2s genotype consistently responded well to avidin seen in the absence of added APC; K2, an H-2k anti-avidin line, responded moderately and B3, and H-2b anti-avidin line, although the most prolific responder in the presence of APC, never responded to antigen in their absence. Z1a, a Lewis rat-derived T cell line specific for myelin basic protein, proliferated well in response to the antigen in the absence of added APC. The present findings demonstrate that some T cells can recognize and respond to native antigens without the mediation of specialized APC.

Production of BSF-1 during an in vivo, T-dependent immune response.

BSF-1, a cytokine produced by some T lymphocyte tumors, has been shown to act with anti-Ig antibodies to stimulate B lymphocyte proliferation, to independently induce resting B lymphocytes to increase their expression of surface Ia antigen, and to induce some activated B lymphocytes to differentiate into IgG1- or IgE-secreting cells. To determine whether BSF-1 might be secreted by normal lymphoid cells in the course of a physiologic immune response, BALB/c mice were injected with an affinity-purified goat antibody to mouse IgD (GaM delta), which induces the generation of a large, polyclonal T-dependent IgG1 response; 4-hr culture supernatants of spleen cells from these mice were prepared, and these supernatants were assayed for BSF-1 activity by analyzing their ability to induce BALB/c nu/nu spleen cells to increase their expression of cell surface Ia in vitro. Culture supernatants of unfractionated spleen cells removed from mice 4 to 8 days after GaM delta antibody injection induced substantial increases in B lymphocyte surface Ia expression; these increases were blocked by a monoclonal anti-BSF-1 antibody. Culture supernatants of spleen cells from untreated BALB/c mice or from untreated or GaM delta antibody-treated BALB/c nu/nu mice induced small to moderate increases in B cell surface Ia expression, and GaM delta antibody itself induced large increases in B cell surface Ia expression; however, these increases were not significantly blocked by a monoclonal anti-BSF-1 antibody. A culture supernatant of T cell-enriched spleen cells from untreated mice induced small increases in B cell surface Ia expression that were inhibited by anti-BSF-1 antibody, as was the larger increase in B cell Ia expression induced by a culture supernatant of T cell-enriched spleen cells from mice sacrificed 3 days after GaM delta injection. On the other hand, T cell-depleted spleen cells from BALB/c mice injected with GaM delta antibody 7 days before sacrifice failed to generate culture supernatants with BSF-1 activity. Supernatants prepared from spleen cells taken from untreated mice or mice treated with GaM delta antibody 1 to 3 days before sacrifice did not block the ability of purified BSF-1 to induce an increase in B cell surface Ia expression, and thus did not contain inhibitors of BSF-1 activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Cyclosporine inhibits macrophage-mediated antigen presentation.

The influence of cyclosporine on antigen-specific, macrophage-dependent T cell activation was analyzed in vitro. Murine T cell activation by antigens derived from Listeria monocytogenes was monitored by the production of interleukin 2. Pretreatment (2 hr, 37 degrees C) of macrophages with cyclosporine resulted in a cell population with a markedly diminished capacity to support the activation of T lymphocytes. When cyclosporine-pretreated macrophages were added to cultures of untreated T cells and antigen, the dose of cyclosporine that produced 50% inhibition (ID50) was 1.5 micrograms/ml, and if antigen was present during the drug pretreatment, the ID50 was 0.6 micrograms/ml. Pretreatment of T cells also inhibited their subsequent activation by antigen and untreated macrophages, but a higher dose of cyclosporine was required to produce similar inhibition (ID50 = 4.4 micrograms/ml). Additional experiments focused on the mechanism of inhibition of antigen presentation when macrophages were pretreated with the drug. The addition of interleukin 1 or indomethacin to the cultures did not alter the inhibitory effect of cyclosporine. Under conditions that produced greater than 90% inhibition of antigen presentation, macrophage surface Ia expression was not altered, and the uptake and catabolism of radiolabeled antigen remained normal. Thus, cyclosporine had profound effects on antigen presentation that appear to be unrelated to decreases in interleukin 1 production, increases in prostaglandin production, decreases in Ia expression, or changes in antigen uptake and catabolism.

In vitro and in vivo B lymphocyte-activating properties of monoclonal anti-delta antibodies. I. Determinants of B lymphocyte-activating properties.

To appreciate better the mechanisms by which B lymphocytes are activated by anti-Ig antibodies, we characterized seven monoclonal mouse allo-antibodies to IgD of the a allotype for their isotypes, fine specificities, IgD-cross-linking abilities, avidities, and abilities to activate B cells in vitro and in vivo. Three of the monoclonal antibodies tested bound to the Fc fragment of IgD with relatively high avidity and were effective at cross-linking IgD, since they precipitated soluble IgD and rapidly capped B cell membrane IgD. These were the only antibodies tested that induced B cell DNA synthesis in vitro and were the most effective antibodies at inducing in vivo increases in B cell size and DNA synthesis and in vitro and in vivo increases in B cell surface Ia expression. Two antibodies bound to the Fd fragment of IgD with relatively high avidity but could not rapidly cap cell membrane IgD or precipitate soluble IgD even in the presence of 2% polyethylene glycol. These high-avidity, poorly cross-linking antibodies were unable to stimulate B cell DNA synthesis in vitro and were much less effective than the first group of anti-delta antibodies at stimulating in vivo increases in B cell DNA synthesis, size, or surface Ia expression or in vitro increases in surface Ia expression. One antibody, which bound to the Fc fragment of IgD with an intermediate avidity, was unable to rapidly cap B cell membrane IgD or precipitate soluble IgD in saline, but could precipitate soluble IgD in the presence of 2% polyethylene glycol. This antibody failed to induce B cell DNA synthesis in vitro and was as effective as the higher-avidity, poorly cross-linking antibodies at stimulating increases in B cell size, surface Ia expression, and DNA synthesis in vivo, and surface Ia expression in vitro. One antibody, which bound to the Fd fragment of IgD with low avidity and was unable to precipitate soluble IgD or to cap cell membrane IgD, had little ability to activate B cells by any of the parameters studied. Each of the monoclonal anti-delta antibodies, regardless of isotype or fine specificity, when bound to agarose to increase its ability to cross-link IgD, was mitogenic for B cells in vitro. None of the monoclonal antibodies to IgD of the a allotype stimulated B cells from b allotype mice to increase their size, surface Ia expression, or synthesis of DNA in vitro or in vivo.(ABSTRACT TRUNCATED AT 400 WORDS)

Influence of allelic polymorphism on the assembly and surface expression of class II MHC (Ia) molecules.

Cell surface Ia expression was examined following transfection of murine alpha and beta class II major histocompatibility complex (MHC) genes into L cells. Although haplotype-matched (e.g., Ak beta Ak alpha) gene pairs yielded high expression in primary transfectants, haplotype-mismatched pairs (e.g., Ak beta Ad alpha) gave unexpectedly low expression. RNA analysis revealed a requirement for greater A beta, and particularly A alpha transcript levels in haplotype-mismatched vs. haplotype-matched transfectants with similar levels of membrane Ia. A beta allelic control of this assembly/expression process was mapped to the NH2-terminal (beta 1) domain, the locus of high intraspecies polymorphism. These data on the effects of allelic variation on Ia levels provide a possible explanation for the strong linkage disequilibrium of A alpha and A beta genes and may account for the current molecular organization of the I region of the MHC.

The modulation of membrane Ia on human B lymphocytes

Using flow cytometry techniques, changes in surface Ia (DR and DS) expression on human B lymphocytes were correlated with changes in the cell cycle following stimulation with anti-μ. The effect of interleukin (IL)-1, IL-2, B-cell growth factor (BCGF), and interferons on Ia expression on resting B cells was also examined. A population of resting B lymphocytes was cultured in vitro with 100 μg/ml of anti-μ and immunofluorescently stained for DR and DS at various times following stimulation. Detectable increases in DR and DS expression were found within 8 hr, and the major increases (twofold and fourfold) in DR and DS expression occurred over the next 48 hr. Using cell cycle inhibitors and propidium iodide staining, it was demonstrated that the enhanced DR and DS expression following anti-μ stimulation began during G 0 to G 1 transition and increased as the cells progressed through G 1 phase. During S and G 2/M phases, there were minimal further increases in surface Ia. Although prolonged exposure of B cells to anti-μ was required for cellular activation, cell size enlargement, and progression into S phase, a brief exposure to anti-μ, insufficient for cellular activation, markedly enhanced Ia expression. Thus anti-μ-stimulated resting human B lymphocytes rapidly increase their surface Ia expression. This increase occurs predominantly prior to entrance into S phase and can occur in the absence of significant cellular activation. Interferons have been reported to modulate surface Ia expression on a human lymphoid cell line and on monocytes and supernatants with BCGF activity to enhance surface Ia expression on murine B cells; however, neither α-interferon, γ-interferon, IL-1, IL-2, nor BCGF modified surface DR expression on normal resting human B cells.

A fish oil diet rich in eicosapentaenoic acid reduces cyclooxygenase metabolites, and suppresses lupus in MRL-lpr mice.

Dietary supplementation of fish oil as the exclusive source of lipid suppresses autoimmune lupus in MRL-lpr mice. This marine oil diet decreases the lymphoid hyperplasia regulated by the lpr gene, prevents an increase in macrophage surface Ia expression, reduces the formation of circulating retroviral gp70 immune complexes, delays the onset of renal disease, and prolongs survival. We show that a fatty acid component uniquely present in fish oil but not in vegetable oil decreases the quantity of dienoic prostaglandin E, thromboxane B, and prostacyclin normally synthesized by multiple tissues, including kidney, lung, and macrophages, and promotes the synthesis of small amounts of trienoic prostaglandin in autoimmune mice. We suggest that this change in endogenous cyclooxygenase metabolite synthesis directly suppresses immunologic and/or inflammatory mediators of murine lupus.