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MHC class II molecules play a central role in the control of adaptive immune responses through selection of the CD4(+) T cell repertoire in the thymus and antigen presentation in the periphery. Inherited susceptibility to autoimmune disorders such as multiple sclerosis, rheumatoid arthritis and IDDM are associated with particular MHC class II alleles. Advent of HLA transgenic mice has helped us in deciphering the role of particular HLA DR and DQ class II molecules in human autoimmune diseases. In mice, the expression of class II is restricted to professional antigen-presenting cells (APC). However, in humans, class II is also expressed on T cells, unlike murine T cells. We have developed new humanized HLA class II transgenic mice expressing class II molecules not only on APC but also on a subset of CD4(+) T cells. The expression of class II on CD4(+) T cells is inducible, and class II(+) CD4(+) T cells can present antigen in the absence of APC. Further, using EAE, a well-established animal model of MS, we tested the functional significance of these class II(+) CD4(+) T cells. DR3.AEo transgenic mice were susceptible to proteolipid protein(91-110)-induced EAE and showed CNS pathology accompanied by widespread inflammation and demyelination seen in human MS patients, suggesting a role for class II(+) CD4(+) T cells in the pathogenesis.

Selection in vivo of potent mAbs to human CD4 useful for immunotherapy, e.g., for the induction of immunological tolerance, is restricted for ethical reasons. We therefore used multiple transgenic mice that lack murine CD4, but express human CD4 specifically on Th cells, and HLA-DR3 as its natural counterligand (CD4/DR3 mice). The injection of CD4/DR3 mice with anti-human CD4 (mAb Max.16H5) before immunization with tetanus toxoid (TT, day 0) totally blocked the formation of specific Abs. This state of unresponsiveness persisted a subsequent boost again performed in the presence of anti-human CD4. When these mice were left untreated for at least 40 days, and were then re-exposed with TT, but in the absence of anti-human CD4, they consistently failed to induce specific Abs (long-term unresponsiveness). Exposure to second party Ags (hen egg lysozyme, human acetylcholine receptor) induced specific Abs comparable with control mice, demonstrating that the anti-CD4-induced unresponsiveness was Ag specific (immunological tolerance). Importantly, the concurrent injection of TT and anti-human CD4 at day 0, followed by another two anti-CD4 treatments, also led to tolerant animals, indicating that tolerance was inducible at the same day as the Ag exposure is provided. We finally demonstrate a limited ability of spleen cells to respond to TT in vitro, indicating that T cells are essentially involved in the maintenance of TT-specific tolerance. These data show for the first time that the human CD4 coreceptor mediates tolerance-inducing signals when triggered by an appropriate ligand in vivo.

MHC class II haplotypes control the specificity of Th immune responses and susceptibility to many autoimmune diseases. Understanding the role of HLA class II haplotypes in immunity is hampered by the lack of animal models expressing these genes as authentic cis-haplotypes. In this study we describe transgenic expression of the autoimmune prone HLA DR3-DQ2 haplotype from a yeast artificial chromosome (YAC) containing an intact similar320-kb region from HLA DRA to DQB2. In YAC-transgenic mice HLA DR and DQ gene products were expressed on B cells, macrophages, and dendritic cells, but not on T cells indicating cell-specific regulation. Positive selection of the CD4 compartment by human class II molecules was 67% efficient in YAC-homozygous mice lacking endogenous class II molecules (Abeta(null/null)) and expressing only murine CD4. A broad range of TCR Vbeta families was used in the peripheral T cell repertoire, which was also purged of Vbeta5-, Vbeta11-, and Vbeta12-bearing T cells by endogenous mouse mammary tumor virus-encoded superantigens. Expression of the HLA DR3-DQ2 haplotype on the Abeta(null/null) background was associated with normal CD8-dependent clearance of virus from influenza-infected mice and development of CD4-dependent protection from otherwise lethal infection with Salmonella typhimurium. HLA DR- and DQ-restricted T cell responses were also elicited following immunization with known T cell determinants presented by these molecules. These findings demonstrate the potential for human MHC class II haplotypes to function efficiently in transgenic mice and should provide valuable tools for developing humanized models of MHC-associated autoimmune diseases.

Mice expressing human CD4 and human MHC II molecules provide a valuable model both for the investigation of the immunopathogenetic role of human autoantigens and for the development of therapeutic strategies based on modulating helper T cell activation in vivo. Here we present a novel mouse model expressing HLA-DR17 (a split antigen of HLA-DR3) together with human CD4 in the absence of murine cd4 (CD4/DR3 mice). Human CD4 accurately replaces murine cd4 within T cells. In particular, the preservation of cd8(+) and CD4(+) T cell subsets distinguishes CD4/DR3 mice from other multiple transgenic models in which the alternative T cell subsets are fundamentally disturbed. Moreover, human CD4 is also faithfully expressed on antigen presenting cells such as dendritic cells and monocyte/macrophages, so that the overall transgenic CD4 expression pattern resembles very closely that of humans. HLA-DR3 expression in the thymus correlates very closely to that of mouse MHC II. In contrast, only 70% of mouse MHC II positive cells in spleen, lymph node, and peripheral blood coexpress HLA-DR3. No significant bias was found with regard to particular leucocytes in this respect. The stimulation of helper T cells clearly depends on the interaction between the human transgene products, since mAbs to HLA-DR and/or CD4 completely blocked in vitro recall responses to tetanus toxoid. CD4/DR3 mice represent a partially humanized animal model which will facilitate studies of DR3-associated autoimmune responses and the in vivo determination of the therapeutic potential of mAbs to human CD4.

We have investigated the activation of the p38 MAPK pathway in response to CD40 engagement in multiple B cell lines and in human tonsillar B cells to define the role of p38 MAPK in proliferation, NF-kappaB activation and gene expression. Cross-linking CD40 rapidly stimulates both p38 MAPK and its downstream effector, MAPKAPK-2. Inhibition of p38 MAPK activity in vivo with the specific cell-permeable inhibitor, SB203580, under conditions that completely prevented MAPKAPK-2 activation, strongly perturbed CD40-induced tonsillar B cell proliferation while potentiating the B cell receptor (BCR)-driven proliferative response. SB203580 also significantly reduced expression of a reporter gene driven by a minimal promoter containing four NF-kappaB elements, indicating a requirement for the p38 MAPK pathway in CD40-induced NF-kappaB activation. However, CD40-mediated NF-kappaB binding was not affected by SB203580, suggesting that NF-kappaB may not be a direct target for the CD40-induced p38 MAPK pathway. In addition, SB203580 selectively reduced CD40-induced CD54/ICAM-1 expression, whereas CD40-dependent expression of CD40 and CD95/Fas and four newly defined CD40-responsive genes cIAP2, TRAF1, TRAF4/CART and DR3 were unaffected. Our observations show that the p38 MAPK pathway is required for CD40-induced proliferation and that CD40 induces gene expression via both p38 MAPK-dependent and -independent pathways.

One hundred and seventy-one unrelated elderly healthy subjects selected according to the Senieur protocol (57 men and 114 women), aged 75-104 years, and 405 healthy individuals (238 men and 167 women), aged 18-65 years, were typed for HLA-A, HLA-B, and HLA-DR antigens. The purpose of the study was to investigate a possible association between HLA antigens and longevity. In the total group of elderly, an increased frequency of HLA-B16 (11.11 vs. 5.43%) and HLA-DR7 (38.33 vs. 15.67%) and a decreased frequency of HLA-B15 (1.75 vs. 5.18%) and HLA-DR4 (11.66 vs. 24.15%) were observed. The HLA-B15DR4 haplotype was not represented (vs. 2.1%), HLA-A1B8 was found with a low frequency (2.9 vs. 4.4%), and HLA-B8DR3 was very rarely found (1.6 vs. 10.1%), whereas the HLA-B13DR7 haplotype was observed with an increased frequency (6.6 vs. 3.3%). These results are in agreement with other published data and suggest that longevity in humans may be influenced by the genetic background.

Major histocompatibility complex (MHC) class II-positive cell lines which lack HLA-DM expression accumulate class II molecules associated with residual invariant (I) chain fragments (class II-associated invariant chain peptides [CLIP]). In vitro, HLA-DM catalyzes CLIP dissociation from class II-CLIP complexes, promoting binding of antigenic peptides. Here the physical interaction of HLA-DM with HLA-DR molecules was investigated. HLA-DM complexes with class II molecules were detectable transiently in cells, peaking at the time when the class II molecules entered the MHC class II compartment. HLA-DR alpha beta dimers newly released from I chain, and those associated with I chain fragments, were found to associate with HLA-DM in vivo. Mature, peptide-loaded DR molecules also associated at a low level. These same species, but not DR-I chain complexes, were also shown to bind to purified HLA-DM molecules in vitro. HLA-DM interaction was quantitatively superior with DR molecules isolated in association with CLIP. DM-DR complexes generated by incubating HLA-DM with purified DR alpha beta CLIP contained virtually no associated CLIP, suggesting that this superior interaction reflects a prolonged HLA-DM association with empty class II dimers after CLIP dissociation. Incubation of peptide-free alpha beta dimers in the presence of HLA-DM was found to prolong their ability to bind subsequently added antigenic peptides. Stabilization of empty class II molecules may be an important property of HLA-DM in facilitating antigen processing.

Background: The ability to secrete blood group antigens into body fluids and secretions is controlled by a single gene on chromosome 19. By means of erythrocyte Lewis (Le) antigen phenotype secretor status can be inferred. An increase prevalence of non-secretors of blood group antigens among coeliac patients has recently been described., Methods: Blood was collected from 112 coeliac patients and 103 controls and tested for secretor status. Secretor status was correlated with human leucocyte antigens (HLA) in coeliac patients, thus evaluating a proposed interaction of susceptibility genes--that is, the secretor gene on chromosome 19 and HLA-linked genes on chromosome 6. Case notes for coeliacs were reviewed with regard to clinical outcome., Results: Of 112 coeliacs who had either Le(a) or Le(b) antigens, 36 (32%) were non-secretors Le(a+, b-), compared with 27% (28) of 103 disease-free controls (P = 0.313). Recessive Lewis phenotype Le(a-, b-) was found in 9% of coeliacs versus 2% of controls. Prevalence of HLA-A1, B8, DR3, and DQ2 was unrelated to secretor status in coeliac versus patients. An increased prevalence of complications and coeliac-associated abnormalities was found in the non-secreting and recessive coeliac groups., Conclusions: This study shows no firm relationship between the non-secretor state and coeliac disease, nor any difference in the distribution of HLA markers among secretor and non-secretor coeliacs. It is unlikely, therefore, that the secretor gene is the much sought-after second coeliac gene.

The HLA-DM alpha and HLA-DM beta genes encode a nonpolymorphic, class II-like molecule that functions by an as yet undefined mechanism in the assembly of processed antigen-HLA class II complexes. Mutant cells that fail to express HLA-DM are deficient in Ag processing. We previously isolated a subcellular compartment in mouse B cells in which functional processed Ag-class II complexes are first formed, referred to as the peptide-loading compartment. Here, evidence is provided that HLA-DM resides in a subcellular compartment with the characteristics of a peptide-loading compartment in a human B lymphoblastoid cell line, but is not required for the intracellular transport of HLA-DR3 molecules to a corresponding compartment in HLA-DM-deficient cells. Thus, the primary defect in HLA-DM-deficient cells does not appear to be a failure in the intracellular trafficking of class II molecules.

The exact incidence of recurrence of membranous nephropathy (MN) after renal transplantation is not well documented because of the limited number of series involving a small number of patients. The aim of this study was to assess the incidence of MN recurrence in our population of renal transplant patients, to identify the risk factors associated with the recurrence, and to analyze the influence of the recurrence on graft and patient survival rates. The recurrence was defined as biopsy-proven MN on the renal graft in a patient whose original disease was MN. Among 1614 consecutive renal transplantations performed from January 1, 1980, to June 1, 1993, the incidence of recurrence was 26.3%, i.e., 5 recurrences out of 19 transplantations. We were unable to show pretransplant epidemiological, immunological, and therapeutic factors associated with recurrence. The HLA DR3 allele was present in 2 patients with recurrence (40%), compared with 3 patients without recurrence (21.4%). The early use of cyclosporine was not associated with a decreased prevalence of MN recurrence. Graft survival was not influenced by the recurrence. Three lymphomas were observed in the 19 transplanted patients with MN as causal nephropathy.

We have shown that there is a subgroup of black recipients who lack DR3 antigen expression and have decreased graft survival in comparison to black recipients who express DR3 antigen. Overall, the 3-year renal graft survival was equivalent between white and black recipients in our series and white recipients were not affected by DR3 antigen expression. We suspect that altered immune activity in the DR3-positive black patients may afford a benefit in overcoming immunologic barriers. This needs further investigation both in light of the possible association of the linked antigens A1-Cw7-B8-DR3 which are associated with loss of suppressor cell activity, as well as the issue of DR3 subtyping. However, there clearly exists the possibility of targeting higher risk groups such as the DR3-negative black recipients for more intense immunosuppressive regimens as well as eliminating pretransplant transfusion of third-party donors. Finally, we must reconsider the question of whether HLA matching is especially punitive to blacks, since matching for broad DR specificities in black recipients does not necessarily match for subtypes unique to blacks. Modifying or de-emphasizing the UNOS point system for organ allocation based on MHC antigen should be seriously considered as a mechanism for increasing the percentage of black kidney transplant recipients.

Here we have examined the connection between IgA deficiency, IgG subclass deficiency, and the absence of alleles of complement C4, and show that IgA deficient subjects who have IgG subclass deficiencies may also have an increased frequency of C4 null alleles. In our group, we found an increased incidence of HLA B38 which might reflect the ethnic composition of the patients tested. While family studies are of primary importance to assess the relationships between histocompatibility antigens and immune deficiency, these studies are complicated by the observation that C4 null alleles are not always inherited with the humoral defect.

The induction of class II antigen (Ag) by interferon-gamma (IFN-gamma) in variants of the K562 cell line has been examined in this study. Following incubation of K562A cells with IFN-gamma, surface expression of HLA-DR molecules was demonstrated by indirect immunofluorescence, confirmed by immunoblotting, and HLA-DR3 Ag specificity identified. HLA-DP and HLA-DRW52 Ag were co-expressed, but no HLA-DQ expression occurred. A variant of this line, designated K1A, spontaneously developed resistance to IFN-gamma induction of class II Ag, but continued to express class I Ag. In a third K562 variant, designated K562B, no class II gene products could be induced. Northern blot analysis indicated that mRNA levels correlated with surface class I and II Ag expression in all of the K562 cell lines. Resistance to IFN-gamma inducible class II Ag expression in K1A cells did not involve changes in IFN-gamma receptor affinity or number but was shown to be due to an inhibitory effect of serum lipid. These results indicate that cells derived from a common parental line may differ in susceptibility to a regulatory mechanism affecting IFN-gamma inducible class II Ag expression.