Periarteriolar Lymphoid Sheath Research Articles

Early passenger leukocyte migration and acute immune reactions in the rat recipient spleen during liver engraftment: with particular emphasis on donor major histocompatibility complex class II+ cells.

After a short course of tacrolimus, Lewis rat liver allografts induce donor-specific nonreactivity in Brown Norway recipients that is immunosuppression-independent after 28 days. To clarify the role of donor major histocompatibility complex (MHC) class II+ cells, we investigated the migration to the recipient splenic T- and B-cell compartments of different subsets of Lewis MHC class II+ passenger leukocytes. The rise and decline of immune activation were monitored in the hepatic allograft and in the host spleen by analyses of BrdU+ (proliferating) leukocytes, TUNEL+ (apoptotic) cells, apoptosis-associated molecules, TH1/TH2 cytokine profiles, and histoimmunocytochemical examination of graft and splenic tissues. Serial flow cytometry studies during the 28-day period of drug-assisted "hepatic tolerogenesis" showed that migratory MHC class II+ cells accounted for less than half of the donor cells in the host spleen. The class II+ cells consisted mostly of B cells that homed to splenic B-cell follicles with only a sparse representation of dendritic cells that were exclusively found in the splenic periarteriolar lymphoid sheath. In parallel studies, transplantation of the less tolerogenic heart produced a diminutive version of the same events, but with far fewer donor cells in the host spleen, evidence of sustained immune activation, and the development of chronic rejection by 100 days. The data are consistent with the paradigm that migration of donor leukocytes is the prime determinant of variable tolerance induction induced by transplantation of the liver and other organs, but without regard for donor MHC class II+ expression.

Golli–myelin basic proteins delineate the nerve distribution of lymphoid organs

The golli–myelin basic proteins (MBPs) have been known to mark the nerve fiber extensions in both the peripheral nervous system (PNS) and the central nervous system. In this paper, we show that the nerve fibers revealed by neurofilament (NF) antibody staining in thymus and spleen, colocalized with golli in the capsular, trabecular (tr), and vasculature (v) systems. In the thymus, the density of these fibers was greater in the medulla than in the cortex. In the spleen, the golli immunoreactive fibers were seen within the capsule (ca), trabeculae, and along the artery tree, as well as the fine nerve fiber networks in the periarteriolar lymphoid sheath (PALS). Golli immunoreactivity appeared to colocalize with ER-TR7, a putative marker of connective tissue in lymphoid organs. However, further examination by Western blot analysis and immunohistochemistry performed on golli “knock out” mice showed that the antigens recognized by these two antibodies were different. The reason for the apparent colocalization of golli and ER-TR7 appears to be due to the close physical association of nerve fibers with connective tissue in these organs. These results suggest that golli immunoreactivity can visualize the distribution of nerve fibers in these lymphoid organs.

Immunohistological study of the immune system cells in paraffin-embedded tissues of conventional pigs

The distribution of different cells of the immune system has been studied in formalin-fixed paraffin-embedded tissues from conventionally reared healthy pigs, using immunohistological techniques. The samples collected were: lungs, tonsils, lymph nodes (mediastinal, mesenteric, inguinal and submandibular), pancreas, spleen, liver, kidney, adrenal gland, ileum and stomach. A total of six primary antibodies anti-CD3, anti-CD79α, Mac 387, anti-lysozyme, anti-CD45RA (3C3/9) and anti-SLA-II-DQ (BL2H5) were used with a standard avidin–biotin peroxidase (ABC) method. Anti-CD3 and anti-CD79α mAb-reacted, respectively with cells located in T cell areas and B cell areas. Mac 387 recognised circulating polymorphonuclear leukocytes, while anti-lysozyme-stained resident macrophages in all tissues. 3C3/9 and BL2H5, were assessed in formalin-fixed paraffin-embedded tissues for the first time. 3C3/9 identified B lymphocytes, in primary follicles and mantle zones, a subpopulation of T cells, especially located in the marginal zone of the spleen and a variable number of immunoblasts, in the germinal centres. BL2H5 reacted with B cells in the mantle zones of the follicles of lymphoid tissues, with dendritic and interdigitating cells in all studied lymphoid tissues and with a variable number of resting and activated T cells in the periarteriolar lymphoid sheath (PALs), marginal zone and red pulp of the spleen. Furthermore, it stained Kupffer and perivascular macrophages in the liver This study represents a detailed histological study of the distribution of the most important subpopulations of immune system cells in conventional, healthy pigs. In our view, these tools should be useful for future comparative studies in disease conditions.

Leishmania donovani: Evolution and Architecture of the Splenic Cellular Immune Response Related to Control of Infection

Melby, P. C., Tabares, A., Restrepo, B. I., Cardona, A. E., McGuff, H. S., and Teale, J. M. 2001. Leishmania donovani: Evolution and architecture of the splenic cellular immune response related to control of infection. Experimental Parasitology99, 17–25. Infection with the protozoan Leishmania donovani in humans is usually subclinical. Parasites probably persist for the life of the host and the low-level infection is controlled by the cellular immune response. To better understand the mechanisms related to the control of infection, we studied the evolution and architecture of the splenic cellular immune response in a murine model that is most representative of human subclinical infection. Following systemic inoculation with L. donovani, the parasites were primarily localized to the macrophage-rich splenic red pulp. There was an initial increase in the numbers of T cells and dendritic cells in the periarteriolar lymphoid sheath and marginal zone, but the red pulp (where parasitized macrophages were prominent) remained free of these cells until later in the course of infection. Thus, T cells did not colocalize with parasitized red pulp macrophages until later in the course of infection. Early in the course of infection, IL-10 production within the marginal zone and TGF-β production by cells in the red pulp were prominent. These macrophage-inhibitory cytokines may contribute to the establishment of the infection and early parasite replication. By day 28 of infection, when the visceral parasite burden began to decline, the number of IL-10-producing spleen cells was back to the baseline level, but IFN-γ production was higher and the number of IL-12-producing cells was increased dramatically. At this time T cells and dendritic cells had moved out of the lymphoid follicle and marginal zone into the red pulp where the parasites were located. These findings therefore suggest that control of infection is associated with IFN-γ and IL-12 production and migration of T cells and dendritic cells to the site of chronic parasitism.

Highly restricted spread of HIV-1 and multiply infected cells within splenic germinal centers.

The tremendous dynamics of HIV infection finds expression in the tempo of sequence diversification. Genetic diversity calculations require the clearance of a majority of infected cells, the obvious predator being anti-HIV immune responses. Indeed, infiltration of germinal centers (GCs) by HIV-specific CD8(+) cytotoxic T lymphocytes has been described. A corollary to this description would be limited diffusion of virus within lymphoid structures. HIV efficiently infects and replicates mainly in activated CD4(+) T lymphoblasts. These cells are found within GCs after their activation in the adjacent periarteriolar lymphoid sheath (PALS). Here GCs and PALS have been dissected from consecutive 10-micrometer sections through splenic tissue from three HIV-1-infected patients. Nested PCR amplification of the two first hypervariable regions of the env gene indicated that 38-78% of sections contained HIV-infected cells. Since there are several hundred CD4(+) T cells per GC section, approximately 0.09-0.64% harbor proviral DNA. Such a low frequency not only suggests that virions on the follicular dendritic cell surfaces do not readily infect adjacent T cells but also indicates highly restricted spread of HIV within GCs and the PALS. Sections were heavily infiltrated by CD8(+) cells, which, together with a large body of extant data, suggests that the majority of infected cells are destroyed by HIV-specific cytotoxic T lymphocytes before becoming productively infected. Finally, sequence analysis revealed that those HIV-positive cells were multiply infected, which helps explain widespread recombination despite a low overall frequency of infected cells.

Alterations in splenic architecture and the localization of anti-double-stranded DNA B cells in aged mice.

Aging is characterized by a decline in humoral immunity and a concommitant increased incidence of anti-DNA and other autoantibodies. To define how the regulation of autoreactive B cells is altered with age, we have used BALB/c mice with an Ig heavy H chain transgene to track the fate of anti-double-stranded (ds) DNA B cells in vivo. In young adult mice, anti-dsDNA B cells are developmentally arrested and excluded from the splenic B cell follicle, whereas in most aged mice they are mature and localize within the B cell follicle. Furthermore, we have detailed global changes in lymphoid architecture that accompany aging: CD4(+) T cells are found not only in the periarteriolar lymphoid sheath, but also in the B cell follicles. Strikingly, these disruptions are similar to those that precede serum anti-dsDNA antibody expression in autoimmune MRL-lpr/lpr mice.

Immunotoxicity of ethyl carbamate in female BALB/c mice: role of esterase and cytochrome P450

Ethyl carbamate, a potent carcinogen, has been characterized to be metabolized by cytochrome P450 (P450) and esterase. It has recently been demonstrated that P450 may activate ethyl carbamate to immunotoxic metabolites. To investigate the role of esterase in ethyl carbamate-induced immunosuppression, mice were pretreated intraperitoneally with an esterase inhibitor, diazinon, at 20 mg/kg 30 min prior to the administration of ethyl carbamate intraperitoneally at 100 and 400 mg/kg for 7 consecutive days. Pretreatment with diazinon completely blocked the serum esterase activity. Histopathologically splenic and thymic atrophy was observed when mice were treated with ethyl carbamate, which was potentiated by the pretreatment with diazinon. In spleen, lymphocytes in the periarteriolar lymphoid sheath and the marginal zone appeared to be depleted in the white pulps. In thymus, ethyl carbamate caused a marked depletion of cells in cortex. The antibody response to sheep red blood cells (SRBCs) was more suppressed by ethyl carbamate in diazinon-pretreated groups than in corn oil-pretreated groups. These results suggest that the metabolism of ethyl carbamate by esterase may be an inactivation pathway in ethyl carbamate-induced immunosuppression. In addition, ethyl N-hydroxycarbamate, a P450 metabolite, suppressed the lymphoproliferative response induced by lipopolysaccharide and concanavalin A in splenocyte cultures. These results indicate that the metabolism of ethyl carbamate by P450 may be an activation pathway in immunosuppression by ethyl carbamate.

Lethal host-versus-graft disease and hypereosinophilia in the absence of MHC I-T-cell interactions.

Neonatal injection of semiallogeneic spleen cells in BALB/c mice induces a self-limited state of chimerism that promotes the differentiation of donor-specific CD4 T cells toward the Th2 phenotype. Here we show that injection of spleen cells from beta2-microglobulin-deficient (BALB/c x C57BL/6) F1 mice into BALB/c newborns with a disrupted beta2-microglobulin (beta2m) gene results in a lethal lymphoproliferative disorder associated with uncontrolled Th2 response, long-term persistence of donor B cells, and sustained blood eosinophilia. Autoimmune manifestations are also enhanced and characterized by a severe autoantibody-mediated glomerulonephritis. Histological examination of the spleen shows a hyperplasia of periarteriolar lymphoid sheaths, with accumulation of eosinophils and basophils, and variable degree of fibrosis. Perivascular lymphoid infiltrates with eosinophils are also found in the lung and are correlated with disease severity. Such abnormalities are almost absent using beta2m-sufficient mice. These data demonstrate that induction of lymphoid chimerism in the absence of MHC class I-T-cell interactions results in a lethal form of host-versus-graft disease that represents a unique model of Th2-dependent chronic inflammatory disease associated with an hypereosinophilic syndrome in mice.

ヒトひ臓白ひ髄，周辺帯の細網性構築

The white pulp (WP) and marginal zone (MZ) constitute the immunologically active compartment of the human spleen. In the WP, there are two distinct regions, the periarteriolar lymphoid sheath (PALS) and the lymph follicle (LF). The basic framework of the PALS, LF and MZ consists of reticulum cells and reticulin fibers. A distinct microenvironment, is formed in the reticular framework of the PALS, LF and MZ, respectively. Immunophenotype of the reticulum cells is heterogeneous in the PALS, LF and MZ. Composition of extracellular matrix proteins of the reticulin fibers is also different in the PALS, LF and MZ. The reticular framework of the PALS, LF and MZ is specialized into heterogeneous components and plays a role in the formation of the distinct microenvironment specific for lymphoid subclasses and the lymphocyte homing and segregation mechanism. In the ontogeny of the PALS, LF and MZ, the development of the heterogeneity of the reticular framework is related with the organization of the PALS, LF and MZ.

The role of CCR7 in TH1 and TH2 cell localization and delivery of B cell help in vivo.

Subsets of murine CD4+ T cells localize to different areas of the spleen after adoptive transfer. Naïve and T helper 1 (TH1) cells, which express the chemokine receptor CCR7, are home to the periarteriolar lymphoid sheath, whereas activated TH2 cells, which lack CCR7, form rings at the periphery of the T cell zones near B cell follicles. Retroviral transduction of TH2 cells with CCR7 forces them to localize in a TH1-like pattern and inhibits their participation in B cell help in vivo but not in vitro. Thus, differential expression of chemokine receptors results in unique cellular migration patterns that are important for effective immune responses.

Distinct migration patterns of naive and effector CD8 T cells in the spleen: correlation with CCR7 receptor expression and chemokine reactivity.

Changes in the migration pattern of lymphocytes represent a key event in the evolution of an immune response since they enable lymphocytes to gain access to infected tissues. We studied the location of virus-specific CD8 T cells in various splenic compartments in response to infection with lymphocytic choriomeningitis virus (LCMV), either in situ or by adoptive cell transfers using T cells from transgenic (tg) mice expressing an LCMV-specific TCR. Naive tg T cells were predominantly localized in the periarteriolar lymphoid sheath, where they proliferated extensively after virus infection. In contrast, in vivo activated effector T cells failed to enter white pulp areas and accumulated in the red pulp. The different homing patterns of naive and effector CD8 T cells in vivo correlated well with their CCR7 chemokine receptor expression and their reactivity to the secondary lymphoid tissue chemokine (SLC). Thus, down-regulation of CCR7 expression on CD8 effector T cells rendered them unre sponsive to SLC, which controls T cell homing into white pulp of spleen and lymph nodes. Exclusion of CD8 effector T cells from these sites may represent an important mechanism to protect professional antigen-presenting cells from cytotoxic T cell attack and thus to prevent a prematuredecline of the immune response.

Expression of the neurotrophin receptor TrkB in rat spleen macrophages.

Increasing evidence suggests that some members of the family of the neurotrophins could be involved in immune system functioning. Both neurotrophins and their tyrosine-kinase signal-transducing receptors, the so-called Trk receptors, have been detected in various lymphoid tissues in a number of species. Nevertheless, their cellular localisation remains unclear in most cases. In this study, we used immunohistochemical techniques to localise TrkB in the rat spleen (from 0 days to 2 years). Cells expressing TrkB-like immunoreactivity were found exclusively within the white pulp of the spleen, along the marginal zone-follicle border and inside the follicles and periarteriolar lymphoid sheaths. These cells probably represented macrophage subpopulations, since they expressed the ED3 rat macrophage antigen. No evidence of TrkB-like protein expression in lymphocytes or follicular dendritic cells could be found. Furthermore, the density of TrkB-immunoreactive cells was observed to increase with age. Although the role of TrkB ligands in these cells remains to be clarified, the present findings provide further evidence for the supposed role of neurotrophins in immune system homeostasis.

Development of immunocompetence of broiler chickens

Subpopulations of T-cells, B-cells, macrophages and ellipsoid-associated reticular cells (EARC) could be demonstrated by immunohistochemical staining early in the development of chicken spleen. However, the typical structures of the spleen, such as the peri-arteriolar lymphoid sheath (PALS) and the ellipsoids with their surrounding ring of macrophages, were only formed around embryonic day (ED) 20. These structures and especially the B-cell compartment, i.e., the peri-ellipsoid lymphoid sheath (PELS) gradually matured during the first week posthatch. Therefore, we analysed at what age broiler chickens could generate a humoral response against the thymus-dependent antigen bovine serum albumin (BSA). Chickens were immunised in ovo (ED16 and ED18) and at 1, 7 and 12 days of age and subsequent BSA-specific immunoglobulin (Ig) M and IgG responses were measured up to 10 days postimmunisation (DPI). No major differences were observed in the relative growth rates, while hatchability was only slightly reduced. Only in chicks immunised on 12 days of age, IgM and IgG responses were high with a normal kinetic pattern. In chicks immunised on 7 days of age, responses were just detectable, but they were absent in chicks immunised in ovo and on the day of hatching (Day 1). In a subsequent experiment, 1-, 7- and 12-day-old chicks were BSA-immunised and Ig responses were measured for a longer period up to the age of 28 days. The IgG response of chicks immunised at 1 day of age was lower and occurred later (from 28 DPI) than the response of chicks immunised at 7 and 14 days of age (from 14 DPI). It was not increased by a booster immunisation on 29 days of age, in contrast to the response of chicks immunised at 7 and 14 days of age. These findings indicate that vaccination at 1 day of age does not activate the B-cell response resulting in antibody production and support the idea that the immune function of the late embryonic and neonatal chickens is not entirely developed due to the incomplete structural organisation of their secondary immune organs.

Analysis of Adjuvant Function by Direct Visualization of Antigen Presentation In Vivo: Endotoxin Promotes Accumulation of Antigen-Bearing Dendritic Cells in the T Cell Areas of Lymphoid Tissue

T cell activation requires exposure to processed Ag and signaling by cytokines and costimulatory ligands. Adjuvants are thought to enhance immunity primarily through up-regulation of the latter signals. Here, we explore the effect of the bacterial adjuvant, endotoxin, on Ag presentation by B cells and dendritic cells (DC). Using an mAb (C4H3) specific for the hen egg lysozyme (HEL) 46-61 determinant bound to I-Ak, we analyze processed Ag expression and the tissue distribution of presenting cells following systemic administration of soluble HEL to mice. In both LPS-responsive and -hyporesponsive mice given endotoxin-containing HEL, B cells rapidly display surface 46-61/I-Ak complexes. In marked contrast, in LPS-hyporesponsive mice, splenic DC show little gain in C4H3 staining. In LPS-responsive animals, interdigitating DC in T cell areas show no staining above background at early times after HEL administration, but C4H3+ DC rapidly accumulate in the outer periarteriolar lymphoid sheaths (PALS) and in follicular areas. Within a few hours, C4H3+ DC appear in the T cell areas, concomitant with a decline in C4H3+ cells in the outer PALS, suggesting migration between these two sites. Endotoxin enhancement of C4H3 staining is seen for both CD8alpha- and CD8alpha+ DC subsets. These data suggest that a major effect of adjuvants is to promote mobilization of Ag-bearing DC to the T areas of lymphoid tissue, and possibly also to enhance Ag processing by these DC. Thus, microbial products promote T cell immunity not only through DC activation for cosignaling, but through improvement in signal 1 delivery.

Detection of phenotypic heterogeneity within the murine splenic vasculature using rat monoclonal antibodies IBL-7/1 and IBL-7/22.

The homing of lymphocytes into various peripheral lymphoid organs involves a complex set of interactions between the circulating lymphoid cells and the local endothelium. While the initial binding and the adhesion processes of lymphocytes leading to their homing to the lymph nodes have thoroughly been studied, relatively little is known about the lymphoid-endothelial interactions taking place in the spleen. Our aim was to isolate rat monoclonal antibodies (MAbs) against the endothelial cells of the mouse spleen. Using splenic stroma derived from irradiated mice as antigen, two new rat MAbs were isolated. The MAb designated as IBL-7/1 bound to the sinus-lining (littoral) cells in the red pulp, marginal zone, and to the T- and B-cell compartments of the white pulp, respectively. However, it did not react with the central arteriole in the periarteriolar lymphoid sheath (PALS). In contrast to this pattern, the IBL-7/22 MAb recognized a shared antigen expressed by the sinusoidal and arterial endothelium. In addition to the endothelial reactivity, the IBL-7/22 MAb also stained the reticular components of the PALS and red pulp, but not that of the follicles. In vivo labelling with fluorescein (FITC)-conjugated IBL-7/1 MAb followed by confocal microscopic analysis revealed that the antigen recognized was expressed on the luminal surface of the sinusoids. The treatment of mice with IBL-7/1 MAb did not result in the altered distribution of T and B cells. These two new MAbs may be valuable tools for the phenotypic analysis of splenic endothelium, and can be used for the identification of various endothelial cell subpopulations of the mouse spleen.

Analysis of murine gammaherpesvirus-68 transcription during lytic and latent infection.

Murine gammaherpesvirus-68 (MHV-68) is a gamma2-herpesvirus that upon experimental infection of laboratory mice establishes a latent infection in B lymphocytes. To date, no virus-encoded gene products have been reported to be expressed during latent infection. In this study, viral transcription has been analysed in a persistently infected B-cell line and abundant and preferential transcription of open reading frame M3 has been identified. Significantly, in situ hybridization analysis of latently infected mouse spleens with probes corresponding to 20 MHV-68 ORFs demonstrated active transcription of a single ORF, corresponding to M3. The kinetics and pattern of transcription of M3 were compared with that of the virally encoded tRNAs (vtRNAs), previously demonstrated to constitute a marker for latent infection in the spleen. Transcription of vtRNAs in splenic tissue could be first detected at 7 days post-inoculation (p.i.) in scattered cells in periarteriolar lymphoid sheaths (PALS). At 10 days p.i., vtRNA transcription was widespread and localized not only to cells in PALS but also to cells within developing germinal centres and from 21 days p.i. expression was detected exclusively within lymphoid follicles. Transcription of vtRNAs could be detected as late as 70 days p.i. In contrast, the histological localization of M3 transcription, which was first detected at 7 days p.i. in scattered cells in PALS, never changed and transcription could not be detected beyond 21 days p.i. These results suggest that M3 is an ORF that is expressed early during the establishment of latency in vivo.

Localization of Splenic B Cells Activated for Switch Recombination by In Situ Hybridization with Iγ1 Switch Transcript and Rad51 Probes

AbstractB cells are activated for switch recombination by signals from Th cells, but the site at which this first occurs in vivo has yet to be identified. By in situ hybridization of splenic sections using riboprobes specific for the Iγ1 switch transcript and Rad51 mRNA, we have visualized B cells that are newly activated for switch recombination and characterized the spatial and temporal patterns of Iγ1 and Rad51 mRNA expression. Within 2 days after immunization with (4-hydroxy-3-nitrophenyl)acetyl-chicken gamma-globulin, expression of Iγ1 switch transcripts and Rad51 mRNA was evident and was localized to B220+ B cells clustered within the T cell-rich periarteriolar lymphoid sheath (PALS) and surrounding follicles. By Ab staining, we have shown previously that cells switching from IgM to IgG expression can be visualized at 3 to 5 days postimmunization and colocalize to clusters of Rad51+ cells. Hybridization of adjacent sections with probes for Cμ and Cγ1 mRNA now shows that switching from μ to γ expression occurs within Rad51+Iγ1+ regions of the PALS and peaks between days 3 and 5. Colocalized expression of Iγ1 and Rad51 transcripts was observed from days 2 through 12 of the immune response. Iγ1 and Rad51 transcripts were down-regulated but still detectable at 12 days postimmunization, when they were evident in peanut agglutinin-positive germinal center B cells. Taken together, these observations show that B cells are first activated for switch recombination in the T cell-rich PALS.

African swine fever: a disease characterized by apoptosis.

The cell tropism, organ distribution and resultant pathology of African swine fever were compared in domestic pigs infected with lethal (Malawi) and sublethal (Malta) isolates of African swine fever virus (ASFV). After infections with both isolates, ASFV was predominantly localized in cells of the mononuclear phagocytic system and was not observed in endothelial cells in lymphoid tissue. More severe tissue destruction and cell depletion, associated with high levels of infected macrophages, were seen in lymphoid tissues from domestic pigs infected with the virulent Malawi isolate compared to the less virulent Malta isolate of ASFV. The abundant lymphocyte death was caused by apoptosis and not necrosis. In the spleen, as early as 3 days post-infection (p.i.), many lymphocytes in the B and T cell areas of the white and red pulp were apoptotic. Apoptosis in the T cells of the periarteriolar lymphoid sheaths in the spleen, however, occurred later, at 5-7 days p.i. In lymph nodes apoptosis was observed in T lymphocytes as early as 4 days p.i. and extended to B lymphocytes in the follicles later in infection. In pigs recovered from infection with the sublethal Malta isolate, virus was found to persist in lymph nodes and tonsils for up to 48 days p.i. and was located in cells, surrounded by apoptotic lymphocytes, in the paracortex of lymph nodes up to 32 days p.i. Taken together, these observations suggest that apoptosis of uninfected lymphocytes was induced by cytokines or apoptotic mediators released from ASFV infected macrophages.

Generation of the Germline Peripheral B Cell Repertoire: VH81X-λ B Cells Are Unable to Complete All Developmental Programs

AbstractThe generation of VH81X heavy chain λ-light chain-expressing B cells (VH81X-λ+ B cells) was studied in VH81X heavy chain transgenic mice as well as in VH81X JH −/− and VH81X JH −/− Ck −/− mice, in which competition resulting from expression of heavy and light chains from the endogenous heavy and κ light chain loci was prevented. We show that although λ light chain gene rearrangements occur normally and give rise to light chains that associate with the transgenic heavy chain to form surface and soluble IgM molecules, further B cell development is almost totally blocked. The few VH81X-λ+ B cells that are generated progress into a mature compartment (expressing surface CD21, CD22, CD23, and low CD24 and having a relatively long life span) but they also have reduced levels of surface Ig receptor and express higher amounts of Fas Ag than VH81X-κ+ B cells. These VH81X-λ+ B cells reach the peripheral lymphoid organs and accumulate in the periarteriolar lymphoid sheath but are unable to generate primary B cell follicles. In other heavy chain transgenic mice (MD2, M167, and M54), λ+ B cells are generated. However, they seem to be preferentially selected in the peripheral repertoire of some transgenic heavy chain mice (M54) but not in others (MD2, M167). These studies show that a crucial selection step is necessary for B cell survival and maintenance in which B cells, similar to T cells, receive signals depending on their clonal receptors.

Splenic para-amyloid material: A possible vasculopathy of the acquired immunodeficiency syndrome

We have observed perivascular para-amyloid in the spleens of acquired immune deficiency syndrome (AIDS) patients at autopsy. Whether this phenomenon is unique to AIDS patients or is a common degenerative phenomenon in the spleen has not been determined. Autopsy spleens from 355 patients (171 AIDS, 184 non-AIDS) were graded for presence of splenic para-amyloid material (SPAM) on a scale of 0 to 3. The average ages of the AIDS and non-AIDS groups were 38.4 and 60.4 years, respectively. All SPAM-positive AIDS cases had age-matched non-AIDS controls. Selected positive cases were examined ultrastructurally. Of the 171 AIDS patients, 55 had SPAM; in 30 cases, it was considered grade 2 or 3. Although none of the non-AIDS cases were graded 2 or 3, eight of them were grade 1. SPAM is highly correlated with AIDS (32.1 v 4.3%; P < .0001), with a specificity of 95.6% and a positive predictive value of 87.3%. These perivascular deposits correspond to areas of periarteriolar lymphoid sheaths and appear to be in continuity with arteriolar adventitia. Ultrastructurally, they contain collagen, long-spaced collagen, fibrillin, and occasional residual cells. No viral particles were noted. SPAM appears to be more prevalent and in greater quantity in AIDS patients. It does not correlate with advanced age; it can be mistaken for amyloid. Its consistent association with the adventitia of vessels raises the possibility of a new vasculopathy of AIDS; it also may be related to follicular involution and hyalinization associated with regression of prior follicular hyperplasia.