Surface Fc Research Articles

Immunoglobulin-Specific Suppressor T Cells

This article has considered evidence that supports the occurrence and functional importance of suppressor T cells that are directed to B cell targets. Cells with these features have been demonstrated in experimental animals and in humans. The designation "suppressor" comes from the serologic phenotype of these cells as well as from their functional property of noncytotoxic inhibition of B cell function. Distinct suppressor T cells with these properties have been identified that effect antigen-, idiotype-, isotype-, and allotype-specific suppression of B cell function. While such cells had been suspected from earlier studies of normal immune responses, the development of monoclonal B cell models using tumor cells has provided a means to readily detect these suppressor T cells and to investigate the mechanisms by which they mediate their effects. Tumor models have proved to be powerful tools in the effort to identify and analyze the elements that underlie the complexity of immune responses. Combined with the insights provided by molecular genetic approaches and flow cytometry, functional and responsive lymphoid tumor cells are being used with increasing frequency to address basic immunoregulatory issues. An important family of suppressor T cells with B cell targets are those that express surface Fc receptors, elaborate immunoglobulin-binding factors, and appear to participate in the regulation of immunoglobulin heavy chain class expression. In addition to their importance in the regulation of heavy chain class expression during normal immune responses, alterations in FcR+ T cells in a number of disease states may provide clues that will lead to a better understanding of disorders of immune regulation.

Partial characterization of different cell types found in the [formula omitted][formula omitted] lymphoreticular tumor based on the presence or absence of surface immunoglobulins and Fc receptor molecules

Cells of Xenopus laevis lymphoreticular tumor induced by tumor tissue transplantation were examined for surface Ig and Fc receptor molecules in order to evaluate the different cell types found in the tumor. Direct immunofluorescent technique, using fluorochrome conjugated rabbit antisera to Xenopus Ig's, detected Ig molecules on the surface of a mean of 31.7 ± 11.3% of cells in tumor suspensions. Most of these molecules were of IgM isotype, reversibly bound to the cell membrane (cytophilic) and could be dissociated by acid pH or overnight cell culturing. In addition integral membrane IgM was detected' on the surface of 10.2 ± 5.9% of the cells. The serum origin of cytophilic Ig's and the cellular origin of integral membrane Ig's were confirmed by analysis of electrophoretic mobility of their heavy chains on SDS-polyacrylamide gels. The existence of Fc receptor molecules on the surface of 48.6 ± 16.6% of the cells was demonstrated by fluorescent staining using heat aggregated FITC labelled IgM or FITC or TRITC labelled antigen-complexed IgY antibodies. 32.2 ± 12.4% and 16.4 ± 6.8% of the cells bore receptors for IgY or receptors for IgM respectively, while 6.3 ± 3.1% carried receptors for both Ig's. Double fluorescent staining revealed that 28.9 ± 4.5% of cells bearing IgM on their surface expressed also receptors for IgY. These results attest to the heterogeneity of the tumor cell population, in respect to the presence or absence of FcR-IgY, FcR-IgM, sIgM, and cytophilic IgM surface molecules.

Different phenotypic variants of the mouse B cell tumor A20/2J are selected by antigen- and mitogen-triggered cytotoxicity of L3T4-positive, I-A-restricted T cell clones.

The L3T4+, Lyt-2-, cloned BALB/c T cell lines 5.9.24 and 5.8.6 are cytotoxic for the BALB/c B cell tumor line A20/2J. The T cell cytotoxicity against A20/2J cells could be triggered either by the specific antigen ovalbumin (OVA), which is recognized by the T cell clones in association with I-Ad determinants, or by the T cell mitogens Con A and rabbit anti-mouse brain (RaMBr) antiserum. Repeated exposure of A20/2J cells to 5.9.24 and 5.8.6 T cell cytotoxicity selected variant cell lines that had developed resistance to cytotoxicity. The variant lines could be classified into four different variant phenotypes of which three were stably maintained in vitro. The type of variant obtained appeared to be related to the nature of the ligand used to trigger T cell cytotoxicity during selection. Cytotoxicity triggered by the antigen OVA generated type 1 variants that expressed abnormally low levels of I-Ad determinants at the cell surface. Type 1 variants were resistant to OVA-triggered 5.9.24 T cell cytotoxicity, but were fully susceptible to cytotoxicity triggered by Con A or RaMBr antiserum. RaMBr-triggered cytotoxicity generated two unique types of variant cell lines: type 3 variants that were deficient in cell surface Fc receptors and resistant to 5.9.24 cytotoxicity only when triggered by RaMBr antiserum, and type 4 variants that were resistant to cytotoxicity triggered by all three ligands. One type 4 variant, the IC-1 cell line, appeared to be resistant to soluble cytotoxic factors released by 5.9.24 T cells after activation by antigen. All of these variant lines retained sensitivity to cytotoxicity by classic Lyt-2+ cytotoxic T lymphocytes (CTL), a finding that indicates that L3T4a+ T cells and Lyt-2+ CTL use different molecules to attack their target cells. The variant phenotypes were inherited by clones derived from the original cell lines. Because the variants were generated without mutagenesis, they are thought to have been derived by the immunoselection of pre-existing variant cells that arose spontaneously in the parental A20/2J cell line. It is postulated that inheritable variation of A20/2J cells may represent changes that normally occur during B cell differentiation in response to T cell signals. The variant A20/2J cell lines described here provide material for the investigation of B cell surface structures that may regulate T-B cell interactions.

Crosslinking of surface immunoglobulin and Fc receptors on B lymphocytes inhibits stimulation of inositol phospholipid breakdown via the antigen receptors.

F(ab')2 fragments of rabbit anti-mouse Ig induce proliferation of murine B lymphocytes, whereas the intact antibodies are not mitogenic. F(ab')2 anti-Ig stimulates the rapid breakdown of inositol phospholipids in B cells, resulting in the prolonged release of inositol (poly)phosphates and diacylglycerol. In marked contrast, intact anti-Ig initially induces a comparable response, which is abrogated after some 30 s. Blocking either the Fc receptors on the B cells or the Fc portion of the antibodies significantly reversed the inhibitory effect. On the other hand, both forms of anti-Ig elicited comparable increases in free cytoplasmic Ca2+ levels in B cells. These results therefore indicate that crosslinkage of Fc and surface Ig receptors on B cells inhibits inositol phospholipid breakdown (but not Ca2+ flux) resulting from ligation of the antigen receptors. Since there is evidence implicating inositol phospholipid breakdown in the induction of cell growth, this effect could provide a biochemical explanation for the known capacity of antigen-antibody complexes to inhibit B cell activation.

A SHARED ANTIGENIC DETERMINANT BETWEEN HUMAN B LYMPHOCYTES AND CARCINOMAS (BLCa)

We have raised a murine IgM monoclonal antibody (MA6) against immunoprecipitate obtained by reacting the serum of an NPC patient with extract of the Burkitt lymphoma cell line, Raji. It reacts against an antigen (BLCa) which is broadly represented on human B lymphoid tissues and cell lines but is different from the functional B-cell markers such as surface immunoglobulins, Ia products, Fc and complement receptors. BLCa was found to occur on lymphoid cell lines representing all stages of B-cell differentiation. These included the pre-B and null-cell lines, Nalm 6 and Reh, the EBV-transformed lymphoid cell lines and the myeloma cell line. MA6 was reactive against all the Burkitt lymphoma cell lines, whether or not these harbored the EBV genomes, with the exception of P3HR-I. The antibody was found to be selectively reactive against a proportion of peripheral blood B lymphocytes and to stain the B-cell-rich primary follicles and mantle zones of secondary follicles in the lymph node. However, MA6 was not reactive against cell lines of T-lymphocyte, myeloid, monocyte fibroblast or epithelial origin. It did, nevertheless selectively stain tumor cells from a variety of carcinoma tissues originating from different anatomical sites, including the nasopharynx.

Migration and differentiation of bone marrow lymphocytes: Development of surface immunoglobulin, Fc receptor, complement receptor, and functional responsiveness as studied with anti-allotype serum

Immunofluorescent studies using fluorescein isothiocyanate-conjugated mouse anti-allotype antibody were carried out to study the migration pattern and the development of surface Ig (SIg), Fc receptor for IgG (FcRγ), and complement receptor (CR) or mouse bone marrow lymphocytes following intravenous injection into congenic mice. After transfer of bone marrow cells from CSW mice into untreated congenic CWB mice, the absolute number of donor-type SIg-bearing (SIg +) cells and the proportion of either FcRγ- or CR-bearing (FcRγ + or CR +) cells in donor-type SIg + cells were evaluated in the recipient spleen and the results were compared with those obtained after the transfer of CSW spleen cells. After injection of donor bone marrow cells, detectable donor-type SIg + cells, although few initially, increased from day 1 to Day 2 and reached a plateau thereafter. The proportion of FcRγ + cells in donor-type SIg + cells, although very low in the donor marrow inoculum, increased progressively after 1 day to reach a maximum at Day 5 (90%). On the other hand, following the transfer of spleen cells, the proportion of FcRγ + cells remained at high levels (90%) for 5 days after transfer. Likewise, the proportion of CR + cells in donor-type SIg + cells was very low (<1%) in the original donor bone marrow cells but high (60%) in the donor spleen cells. However, in transferring bone marrow cells this proportion also increased in the recipient spleen to reach a maximum (49%) at Day 5 although it was lower compared to the percentage of FcRγ + cells in donor SIg + cells. Furthermore, the ability of functional responsiveness to antigen was also examined in the same system by detecting plaque-forming cells (PFC) from donor origin. In transferring donor bone marrow cells into recipient, the participation of donor cells in the PFC response was very low when the recipients were primed with sheep red blood cells at Day 3 after transfer. However, when the recipients were primed at Days 7 to 21 after transfer, increasing numbers of the donor marrow-derived cells were involved in the PFC response. Thus, the present study demonstrates that the bone marrow-derived lymphocytes, albeit lacking both distinctive surface receptors (IgM, FcRγ, CR) and the functional responsiveness to antigen, continue their development along the B-cell lineage after migrating into the spleen, as evidenced by the surface receptor expression and participation in the antibody response.

Amblyomma americanum: Requirement for host Fc receptors in antibody-mediated acquired immune resistance to ticks

Guinea pig recipients of anti-tick immune serum or immune peritoneal exudate cells expressed 25 and 30% tick rejection, respectively, when challenged with Amblyomma americanum larval ticks. Previous studies have shown that IgG 1 antibodies are responsible for the ability of immune serum to transfer resistance to ticks and to mediate the accompanying, and required, cutaneous basophil response. Since IgG 1 antibodies induce mast cell-mediated passive cutaneous anaphylaxis and cutaneous basophil responses by interaction with cell surface Fc receptors, we investigated whether host Fc receptors were involved in the mechanism of antibody-mediated immune resistance to ticks. Recipients of immune serum pretreated intravenously with rabbit IgG failed to express resistance when challenged. In contrast, recipients of immune peritoneal exudate cells similarly pretreated expressed normal resistance. Sheep IgG had no inhibitory effect on the transfer of resistance by either immune serum or peritoneal exudate cells. Furthermore, recipients of immune serum pretreated with the Fc fragment from papain digestion of rabbit IgG failed to express resistance when challenged with ticks. Rabbit Fab and sheep Fc and Fab had no effect on the transfer of resistance by immune serum. Purity of rabbit Fc preparations was verified by the ability to inhibit mast cell-mediated passive cutaneous anaphylaxis due to high-titered IgG 1 antiovalbumin antibodies. Rabbit Fab and sheep Fc fractions did not inhibit passive cutaneous anaphylaxis reactions. These findings suggest that immunoglobulin Fc receptors on host cells, such as mast cells and basophils, are required for antibody-mediated immune rejection of ticks from guinea pigs.

Bone marrow-derived macrophages: development and regulation of differentiation markers by colony-stimulating factor and interferons.

To investigate the role of specific cytokines in the development of the fully mature macrophage, we have employed murine bone marrow cells that were grown in the presence of CSF-1, a colony-stimulating factor that has been shown to induce the proliferation and differentiation of macrophages from their precursor cells. The CSF-1 employed in these studies was partially purified to ensure removal of contaminating interferon (IFN) from the preparations. After 1 to 2 wk in the presence of the partially purified CSF-1, the adherent macrophages were removed from flasks enzymatically and were recultured at known densities in the absence of CSF-1. Cell surface antigens (Mac-1 and Ia) and Fc receptor capacity (as assessed by Fc-mediated phagocytosis) were examined as markers of macrophage differentiation. Basal levels of Fc receptor capacity and Mac-1 antigen were markedly influenced by exposure to CSF-1, and appear to be modulated by CSF-induced, macrophage-derived IFN. When the bone marrow-derived macrophages were exposed to exogenous IFN in the absence of CSF-1, they proved to be extremely inducible with respect to Fc-mediated phagocytosis (IFN-beta and rIFN-gamma) and Ia antigen expression (rIFN-gamma) when compared with thioglycollate-elicited macrophages. Thus, macrophage growth factors, such as CSF-1, promote macrophage maturation by inducing the production of autostimulatory signals, such as macrophage-derived IFN. In addition, exogenous cytokine stimuli, such as IFN-gamma, further amplify the differentiative potential of these cells. Bone marrow-derived macrophages, propagated under well-defined conditions and never exposed to eliciting agents, provide a powerful model for studying the role of cytokines, such as CSF-1 and IFN, in the differentiative pathway of macrophages.

Identification of soluble Fc receptors in mouse serum and the conditioned medium of stimulated B cells.

We have evaluated the expression of surface Fc gamma 2b/gamma 1R by lipopolysaccharide (LPS)-activated murine spleen cells, the release of soluble Fc gamma 2b/gamma 1R by activated spleen cells, and the presence of circulating Fc gamma 2b/gamma 1R in mouse serum. LPS activation of murine spleen cells and a cloned B cell line, BCL-1 CW 13.20-3B3, resulted in a 5-10-fold increase in surface Fc gamma 2b/gamma 1R and the concominant appearance in the culture medium of a soluble molecule that is antigenically related to the Fc gamma 2b/gamma 1R. The increase in cell-associated and soluble Fc gamma 2b/gamma 1R after LPS activation is attributable primarily to B cells. Circulating Fc gamma 2b/gamma 1R was also detected in normal mouse serum at a concentration of 10(-9) to 10(-8) M. Levels of circulating Fc gamma 2b/gamma 1R increase with the age of the animals, and were low in adult germ-free mice and elevated in young mice with certain autoimmune diseases. The circulating Fc gamma 2b/gamma 1R bound to IgG-Sepharose, and was partially purified by affinity chromatography on 2.4G2 Fab-Sepharose. After radiolabeling and immunoprecipitation with rabbit anti-Fc gamma 2b/gamma 1R serum, one component of Mr 48,000, was detected.

Fc gamma receptor-mediated suppression of gamma-interferon-induced Ia antigen expression on a murine macrophage-like cell line (P338D1).

A variant (HS-1) of a murine macrophage cell line (P388D1) was obtained by cell cluster technique based on the Ia antigen expression induced by lymphokines. Receptors for both IgG2a and IgG2b but no detectable I-Ad are expressed on the surface of the majority of HS-1 cells. Exposure of HS-1 cell to concanavalin A supernatant or recombinant IFN-gamma resulted in the induction of I-Ad antigens on greater than 90% of the cells within 48 hr. The effects of lymphokines were transient and dependent on the synthesis of messenger RNA because the removal of lymphokines or the presence of actinomycin D both blocked Ia expression. The prior or simultaneous binding of monoclonal IgG2a or IgG2b antibodies complexed with sheep erythrocytes to respective cell surface Fc gamma R suppressed the Ia antigen inducing activity of lymphokines. Neither antibody nor antigen alone could suppress the effect of lymphokines. Inhibitors of phospholipase A2 or cyclooxygenase, which have been shown previously to suppress Fc gamma 2bR, but not Fc gamma 2aR, triggered activation of the adenylate cyclase system and reversed Fc gamma 2bR- but not Fc gamma 2aR-mediated suppression of IFN-gamma-induced Ia antigen expression.

An immunoblotting technique for the detection of bound and secreted bacterial Fc receptors

A rapid semiquantitative procedure that enables bacteria to be screened for surface or secreted receptors for the Fc region of human IgG is described. Surface Fc receptors were detected by direct transfer of bacterial colonies to nitrocellulose by electroblotting and then probing with 125I-labeled human IgG in the presence of a two fold molar excess of unlabeled F(ab′) 2fragments. The blots were exposed to X-ray film and the intensity of the resulting autoradiograph was a measure of surface Fc receptors expression. This procedure reliably distinguished Staphylococcus aureus strains which expressed different levels of surface Fc receptors. When applied to the study of group A streptococci, a number of Fc receptor-positive strains were identified. Unlike the homogeneous Fc receptor expression on individual colonies of the staphylococcal strains, a wide variation in the level of Fc receptor expression was observed within a given streptococcal strain. Group A streptococcal substrains which expressed high and low levels of surface Fc receptors could be isolated from replica plates. Secreted Fc receptors were measured by a simple modification of the blotting procedure in which the nitrocellulose was placed on the opposite side of the agar from the bacterial colonies. Secreted Fc receptors was electroblotted through the agar onto nitrocellulose and probed as described above. This approach readily detected nanogram quantities of secreted type I Fc receptor (protein A) from the Staphylococcus aureus Cowan strain. None of the group A streptococcal strains tested were found to secrete detectable quantities of Fc receptors.

The mode of action of antibody in neutrophil bactericidal activity against highly pathogenic group-B streptococci.

An investigation was undertaken into the post-phagocytic action of specific antibody in initiating neutrophil bactericidal activity against highly pathogenic group-B streptococci that survive within these cells. Specific antibody appears to gain access to the interior of the neutrophil and binds to the intracellular bacteria. Activation of Fc receptors on the neutrophil surface is not sufficient to initiate bactericidal activity, but the antibody may utilise the surface Fc receptors to gain access to the ingested organisms. Fusion of the lysosomes with the phagosomes containing the streptococci occurs normally in the cells, and proceeds in both the presence and absence of specific antibody. The organisms are resistant, however, to the microbicidal agents of lysosomes. A significant role is demonstrated for specific antibody in "masking" protective determinants on the bacterial surface during the destruction of these organisms by neutrophils. The relevance of antibody entry into neutrophils in relation to the treatment of bacterial infection is discussed.

Varicella-Zoster Virus-Induced Transformation of Mammalian Cells in Vitro

A mixture of varicella-zoster virus-infected human embryonic lung fibroblasts and hamster embryo cells produced foci of morphologically transformed cells after several weeks of incubation. These transformed cells exhibited virus-specific antigens by immunofluorescence and developed surface Fc receptors. They induced aggressive fibrosarcomas when injected back into inbred hamsters. Cells derived from hamster tumor tissue exhibited similar properties. The tumor-bearing hamsters develop antibodies specific for varicella-zoster virus (VZV) antigens. Cell lines derived from both the original transformants and explanted hamster tumor tissue have varying growth properties. All maintain indefinite growth. All eventually lose varicella-zoster virus-specific immunofluorescence. None retain VZV-specific DNA sequences as determined by dot blot and Southern blot hybridization using radiolabeled whole VZV DNA and cloned VZV DNA fragments as a probe. A few transformed and tumor cell lines frozen relatively soon after isolation and stored in liquid nitrogen were also thawed, replicated to mass culture, and analyzed for VZV-specific DNA sequences. Hybridization with radiolabeled whole VZV DNA initially suggested that some of these cell lines did contain virus-specific DNA sequences. However, hybridization with cloned VZV DNA fragments radiolabeled in vitro and representing greater than 95% of the virus genome was negative. Karyotyping of these "positive" transformed cells indicated that they are of human and not hamster origin. The positive hybridization with whole VZV DNA therefore most likely represented contamination of the probe by host DNA sequences. The cells that survived freezing then were predominantly transformants of human origin. Attempts to repeat the transformation of hamster embryo and baby hamster kidney cells with laboratory-passaged VZV strains have been unsuccessful. Similarly, we have been unable to transform cells with whole VZV DNA or cloned VZV DNA fragments, although whole VZV DNA is demonstrably infectious. Apparently, transformation of cells by the varicella-zoster virus is a very rare event and one that may require a recent clinical isolate. Fresh clinical isolates of varicella-zoster virus are seemingly able to transform mammalian cells in vitro. The transformed cells have malignant properties and are capable of indefinite growth. Although VZV gene function can be detected early after transformation, there is no evidence that a VZV-specific protein product is required. Transformation of mammalian cells by varicella-zoster virus apparently occurs through a "hit-and-run" mechanism.

Varicella-zoster virus-induced transformation of mammalian cells in vitro.

A mixture of varicella-zoster virus-infected human embryonic lung fibroblasts and hamster embryo cells produced foci of morphologically transformed cells after several weeks of incubation. These transformed cells exhibited virus-specific antigens by immunofluorescence and developed surface Fc receptors. They induced aggressive fibrosarcomas when injected back into inbred hamsters. Cells derived from hamster tumor tissue exhibited similar properties. The tumor-bearing hamsters develop antibodies specific for varicella-zoster virus (VZV) antigens. Cell lines derived from both the original transformants and explanted hamster tumor tissue have varying growth properties. All maintain indefinite growth. All eventually lose varicella-zoster virus-specific immunofluorescence. None retain VZV-specific DNA sequences as determined by dot blot and Southern blot hybridization using radiolabeled whole VZV DNA and cloned VZV DNA fragments as a probe. A few transformed and tumor cell lines frozen relatively soon after isolation and stored in liquid nitrogen were also thawed, replicated to mass culture, and analyzed for VZV-specific DNA sequences. Hybridization with radiolabeled whole VZV DNA initially suggested that some of these cell lines did contain virus-specific DNA sequences. However, hybridization with cloned VZV DNA fragments radiolabeled in vitro and representing greater than 95% of the virus genome was negative. Karyotyping of these "positive" transformed cells indicated that they are of human and not hamster origin. The positive hybridization with whole VZV DNA therefore most likely represented contamination of the probe by host DNA sequences. The cells that survived freezing then were predominantly transformants of human origin. Attempts to repeat the transformation of hamster embryo and baby hamster kidney cells with laboratory-passaged VZV strains have been unsuccessful. Similarly, we have been unable to transform cells with whole VZV DNA or cloned VZV DNA fragments, although whole VZV DNA is demonstrably infectious. Apparently, transformation of cells by the varicella-zoster virus is a very rare event and one that may require a recent clinical isolate. Fresh clinical isolates of varicella-zoster virus are seemingly able to transform mammalian cells in vitro. The transformed cells have malignant properties and are capable of indefinite growth. Although VZV gene function can be detected early after transformation, there is no evidence that a VZV-specific protein product is required. Transformation of mammalian cells by varicella-zoster virus apparently occurs through a "hit-and-run" mechanism.

Effects of 89 Sr on the Production and Maturation of Small Lymphocytes Bearing Surface Immunoglobulin, Fc, and Complement Receptors in Mice

Ten-week-old C57B1/6J mice were given an intraperitoneal injection of 100 microCi radiostrontium (89Sr). One and two weeks following injection, the cellular composition of marrow and spleen was examined for cellularity, types of lymphoid cells, and incidences of small lymphocytes bearing sIgM, FcR, and CR. Strontium-89 treatment yielded a significant cell depletion in marrow, whereas spleen cellularity initially increased before returning to normal level in the second week. The increase in spleen cellularity was showed by pulse DNA labeling to be due to local production and not to influx from elsewhere. The percentage of medium and large lymphocytes, precursors of small lymphocytes, increased from 4% in the control spleen to 22% in the 89Sr-treated spleen. The incidences of small lymphocytes bearing sIgM, FcR, and CR were lower than normal levels with the exception of a substantial increase of FcR+ small lymphocytes in the spleen 2 weeks following 89Sr injection. Double-labeling studies, combining rosetting for surface receptors and DNA labeling for cell age, showed that small lymphocytes bearing sIgM, FcR, and CR form part of the major population of indigenous rapidly renewed cells in 89Sr-treated spleen.

Cultured human and rat oligodendrocytes and rat schwann cells do not have immune response gene associated antigen (Ia) on their surface

In order to determine if oligodendrocytes or Schwann cells had surface immune response gene associated antigen (Ia), we studied the binding of: (a) mouse monoclonal antibodies to rat Ia, to cultures of rat oligodendrocytes and Schwann cells; and, (b) mouse monoclonal antibodies to human Ia, to cultures of human oligodendrocytes employing radioimmunoassay and indirect immunofluorescence. Cells were identified using phenotypic markers; rabbit anti-galactocerebroside (GalC) for oligodendrocytes; rabbit anti-GalC and rabbit anti-Schwann cell for Schwann cells; rabbit anti-glial fibrillary acidic protein for astrocytes; rabbit anti-fibronectin for fibroblasts and leptomeningeal cells, and the capacity to ingest latex particles for macrophage-microglia. Ia could not be detected on the surface of oligodendrocytes, Schwann cells, astrocytes, fibroblasts, or leptomeningeal cells. A small number of latex ingesting cells bound anti-Ia even after blocking of surface Fc receptors.

An avidin-biotin-peroxidase method for Fc receptors on macrophages isolated from and in sections of rat lung.

Receptors for the Fc region of immunoglobulin G (Fc receptors) were detected on pulmonary macrophages by adapting an avidin-biotin-peroxidase technique to isolated cells and sections of rat lung. After incubation with soluble rabbit immunoglobulin G (IgG), surface bound IgG was identified consistently and reproducibly on glass-adherent pulmonary macrophages and on macrophages in tissue sections made from incubated lung slices. Control experiments indicated that binding was specifically mediated by surface Fc receptors. This method may be useful for identifying macrophages in intact tissues.

Spontaneous in vitro occurrence and long-term culture of murine B lymphoblast cell lines.

Under simple culture conditions, in vitro culture of T cell-depleted splenic mononuclear cells reliably promotes the outgrowth of B lymphoblasts. Such cells, termed BLY1, can be propagated as long-term B cell lines but are nontumorigenic in syngeneic recipients. The phenotype of BLy1 cells is unusual. They express certain B cell markers, including surface mu-lambda, I-Ak, and C3 and Fc receptors; however, delta heavy chain and kappa light chain production is absent. Although the cells do not express Thy-1 or Lyt-2, Lyt-1 is readily demonstrable. These distinctive features of BLy1 cells thus resemble a recently described B cell subset prominent early in ontogeny, and in the B cell defect of NZB mice.

Immunological markers of human mononuclear cells

The immune response to an antigenic challenge results from complex intercellular communications between several populations of lymphoreticular cells. Immunocompetent cells are derived from a common stem cell precursor and develop along two distinct pathways. The T-cell lineage (T-lymphocytes) originates in the thymus and mediates cellular immunity, whereas B-cells (bone marrow derived lymphocytes) mature into antibody producing cells. The maturation of B-cells into plasmacytes is under the control of two regulatory T-cell subsets. Helper T-cells (TH) induce the differentiation of B-cells into antibody producing cells. In contrast, suppressor T-cells (TS) inhibit this maturation process. Therefore, immunoregulation results from a delicate balance between inducer and suppressor T-cell subsets. The various lymphocyte populations and subsets express specific membrane glycoproteins (surface antigens and receptors) which therefore allow their identification by cell surface marker analysis. The advent of hybridoma antibodies directed against unique integral membrane proteins has provided a powerful tool for characterizing lymphocyte subsets and for understanding the antigenic changes that occur during their ontogeny. Pre-B cells produce intracytoplasmic mu chains. B cells express surface immunoglobulins, Ia antigens, Fc receptors and complement receptors. Plasmacytes contain intracytoplasmic immunoglobulins. T-cells form spontaneous rosettes with sheep erythrocytes. Helper T-cells express a specific surface antigen (T4), whereas cytotoxic/suppressor T-cells bear another membrane marker (T8). The use of such immunological markers has greatly facilitated the dissection of various human diseases, such as lymphoproliferative malignancies, autoimmune disorders and immunodeficiencies.

A lymphoblastoid cell line with high phagocytic activity established from peripheral blood of a patient with chronic myelocytic leukemia in blast crisis.

A human hematopoietic cell line (K-23-M) was established from a patient with chronic myelocytic leukemia in blast crisis. Morphologically, the cultured cells were lymphoblastoid cells that produced IgA and were Epstein-Barr viral nuclear antigen positive. But they showed high phagocytic activity to glutaraldehyde-treated sheep red cells and had properties of a monocyte or macrophage that included surface Fc receptors, alpha-naphthyl butyrate esterase positivity blocked by NaF, migration in soft agar and the ability to attach to a glass surface. Lysozyme secretion was absent, and chromosomes were diploid and Ph1 negative. This cell line is unique in that it has strong phagocytic activity. Its existence shows that lymphoblastoid cell line may be a more important cell line for the study of human hematopoietic cells than previously has been believed.