H-2 haplotypes, genes and antigens: second listing. II. The H-2 complex

The Naming of Memory T-Cell Subsets

With ever-improving methods of cell characterization, the field of immunology has enjoyed unprecedented opportunities to resolve distinctions between lymphocyte populations. However, this has led to a proliferation of "subset" designations that threatens to complicate and confuse clear identification of populations that share critical functional traits. This article discusses some of the challenges associated with a uniform approach to assigning subset designations to memory T-cell populations.

Beta Cell Dedifferentiation Induced by IRE1α Deletion Prevents Type 1 Diabetes

Immune-mediated destruction of insulin-producing β cells causes type 1 diabetes (T1D). However, how β cells participate in their own destruction during the disease process is poorly understood. Here, we report that modulating the unfolded protein response (UPR) in β cells of non-obese diabetic (NOD) mice by deleting the UPR sensor IRE1α prior to insulitis induced a transient dedifferentiation of β cells, resulting in substantially reduced islet immune cell infiltration and β cell apoptosis. Single-cell and whole-islet transcriptomics analyses of immature β cells revealed remarkably diminished expression of β cell autoantigens and MHC class I components, and upregulation of immune inhibitory markers. IRE1α-deficient mice exhibited significantly fewer cytotoxic CD8⁺ T cells in their pancreata, and adoptive transfer of their total T cells did not induce diabetes in Rag1^-/- mice. Our results indicate that inducing β cell dedifferentiation, prior to insulitis, allows these cells to escape immune-mediated destruction and may be used as a novel preventive strategy for T1D in high-risk individuals.

The Attenuated Live Yellow Fever Virus 17D Infects the Thymus and Induces Thymic Transcriptional Modifications of Immunomodulatory Genes in C57BL/6 and BALB/C Mice

Thymus is involved in induction of self-tolerance in T lymphocytes, particularly due to Aire activity. In peripheral tissues, Treg cells and immunomodulatory molecules, like the major histocompatibility complex (MHC) class Ib molecules, are essential for maintenance of autotolerance during immune responses. Viral infections can trigger autoimmunity and modify thymic function, and YFV17D immunization has been associated with the onset of autoimmunity, being contraindicated in patients with thymic disorders. Aiming to study the influence of YFV17D immunization on the transcriptional profiles of immunomodulatory genes in thymus, we evaluated the gene expression of AIRE, FOXP3, H2-Q7 (Qa-2/HLA-G), H2-T23 (Qa-1/HLA-E), H2-Q10, and H2-K1 following immunization with 10,000 LD50 of YFV17D in C57BL/6 and BALB/c mice. The YFV17D virus replicated in thymus and induced the expression of H2-Q7 (Qa-2/HLA-G) and H2-T23 (Qa-1/HLA-E) transcripts and repressed the expression of AIRE and FOXP3. Transcriptional expression varied according to tissue and mouse strain analyzed. Expression of H2-T23 (Qa-1/HLA-E) and FOXP3 was induced in thymus and liver of C57BL/6 mice, which exhibited defective control of viral load, suggesting a higher susceptibility to YFV17D infection. Since the immunization with YFV17D modulated thymus gene expression in genetically predisposed individuals, the vaccine may be related to the onset of autoimmunity disorders.

The path to reactivation of antitumor immunity and checkpoint immunotherapy

Cancer immunology has recently made major therapeutic inroads that represent clinical application of basic insights into mechanisms that govern immunity against tumors. Research into fundamental elements of T-cell and natural killer-cell biology, including the basis of antigen recognition, activation, proliferation, and survival, has informed the design of new therapeutic approaches to augment the body's natural anticancer immune response. Here, we describe some of the key steps that have provided the foundation for current strategies of immunotherapy.

Differential transcript profiles of MHC class Ib(Qa-1, Qa-2, and Qa-10) and Aire genes during the ontogeny of thymus and other tissues

Qa-2 and Qa-1 are murine nonclassical MHC class I molecules involved in the modulation of immune responses by interacting with T CD8(+) and NK cell inhibitory receptors. During thymic education, the Aire gene imposes the expression of thousands of tissue-related antigens in the thymic medulla, permitting the negative selection events. Aiming to characterize the transcriptional profiles of nonclassical MHC class I genes in spatial-temporal association with the Aire expression, we evaluated the gene expression of H2-Q7(Qa-2), H2-T23(Qa-1), H2-Q10(Qa-10), and Aire during fetal and postnatal development of thymus and other tissues. In the thymus, H2-Q7(Qa-2) transcripts were detected at high levels throughout development and were positively correlated with Aire expression during fetal ages. H2-Q7(Qa-2) and H2-T23(Qa-1) showed distinct expression patterns with gradual increasing levels according to age in most tissues analyzed. H2-Q10(Qa-10) was preferentially expressed by the liver. The Aire transcriptional profile showed increased levels during the fetal period and was detectable in postnatal ages in the thymus. Overall, nonclassical MHC class I genes started to be expressed early during the ontogeny. Their levels varied according to age, tissue, and mouse strain analyzed. This differential expression may contribute to the distinct patterns of mouse susceptibility/resistance to infectious and noninfectious disorders.

A survey of H2 gene sequences, including new wild-derived genes

A comprehensive collection of mouse major histocompatibility complex (MHC) promoter and exon 2 sequences is here presented and analysed. It covers the three best known class II genes and one class I gene, and includes new wild mouse sequences from the 'w' back-cross strains and from the Jackson collection. All sequences are in GenBank, and the new exon sequences largely confirm previous typing by serology and immune function. As in human leucocyte antigen (HLA), the overall nucleotide diversity is higher in the class II genes, in keeping with their more diverse function. Diversity along the promoters is highest in the region of known transcription factor binding, most notably in and around the CRE and rCAAT sequences. This distribution parallels that of maximum single nucleotide polymorphism impact previously obtained with reporter constructs. Taking into account the low nucleotide diversity of the CIITA promoter, we conclude that MHC promoters are likely to have diversified through co-evolution with their exons, while themselves also directly subject to natural selection. The H2Eb(p) alleles form a distinct group, associated with their lack of the recombination hot spot located between exon 2 and exon 3. The collection is expected to prove useful in guiding functional and evolutionary studies.

An MHC-linked locus modulates thymic differentiation of CD4+CD25+Foxp3+ regulatory T lymphocytes

CD4+CD25+Foxp3+ regulatory T lymphocytes are crucial for maintenance of immunological tolerance to self and innocuous non-self, are known to modulate immunity to tumors and infectious agents and can induce transplantation tolerance. Surprisingly, only a single genetic polymorphism is known to modulate regulatory T cell (Treg) development in the thymus, leading to a lethal autoimmune disorder. Here, we show that considerably different levels of Tregs are found in the thymi of distinct common laboratory mouse strains. We demonstrate that distinct levels of phenotypically and functionally identical Tregs develop with similar kinetics in the studied mice, that the responsible locus acts in a thymocyte-intrinsic manner and that levels of thymic Foxp3+ Tregs correlate to those found in the periphery. Using several congenic mouse strains, we mapped one of the at least two genetic loci capable of quantitatively modulating thymic Treg development to a Collapse

Key Words

• animals
• antigens, surface
• metabolism
• cd4-positive t-lymphocytes
• cell differentiation
• genetics
• immunology
• female
• forkhead transcription factors
• genes, mhc class ii
• physiology
• interleukin-2 receptor alpha subunit
• mice
• mice, inbred strains
• t-lymphocytes, regulatory
• cytology
• telomere
• thymus gland

Collapse

MESH Headings

• Animals
• Antigens, Surface/metabolism
• CD4-Positive T-Lymphocytes/metabolism
• Cell Differentiation/genetics
• Cell Differentiation/immunology
• Female
• Forkhead Transcription Factors/metabolism
• Genes, MHC Class II/genetics
• Genes, MHC Class II/physiology
• Interleukin-2 Receptor alpha Subunit/metabolism
• Mice
• Mice, Inbred Strains/immunology
• T-Lymphocytes, Regulatory/cytology
• T-Lymphocytes, Regulatory/immunology
• Telomere/physiology
• Thymus Gland/cytology
• Thymus Gland/immunology

Collapse

Grants Collapse

Affiliation(s)

Julie Tellier Centre de Physiopathologie de Toulouse Purpan INSERM : U563IFR30Université Paul SabatierInstitut Claude de Préval Toulouse, FR
Joost PM van Meerwijk Centre de Physiopathologie de Toulouse Purpan INSERM : U563IFR30Université Paul SabatierInstitut Claude de Préval Toulouse, FR Institut universitaire de France and Faculty of life-sciences (UFR-SVT) Université Paul SabatierToulouse,FR
Paola Romagnoli Centre de Physiopathologie de Toulouse Purpan INSERM : U563IFR30Université Paul SabatierInstitut Claude de Préval Toulouse, FR

Collapse

Rejection patterns in allogeneic uterus transplantation in the mouse

BACKGROUND

Transplantation of the uterus in the mouse has been developed as a model system for research towards human uterine transplantation. Previous studies in a mouse model have demonstrated that a syngeneic uterus transplant can give rise to normal offspring. The aim of this study was to characterize the time course of rejection in a fully allogeneic mouse uterus transplantation model.

METHODS

Uteri of BALB/c mice were transplanted to a heterotopic position in C57BL/6 recipients, whose native uteri were left in situ. The blood flow of the uteri, their gross appearance and general histology and the density of T-lymphocytes were examined on postoperative days 2-28.

RESULTS

Macroscopic signs of rejection were apparent from day 5. At the light microscopy level, minimal inflammatory changes were seen from day 5 and massive inflammation was seen from day 10 to day 15. At day 28, necrosis and fibrosis were seen. The density of T-lymphocytes (CD3(+)) was increased in the grafted uterus from day 2 in the myometrium and from day 5 in the endometrium. Blood flow in the grafted uteri was reduced from day 15.

CONCLUSION

A murine model to study rejection of allogeneic uterus transplants was characterized. Signs of rejection were seen from day 2 to day 5 and severe rejection was seen from day 10 to day 15. The data will be useful in future studies on immunosuppressants in this model.

Epistatic suppression of systemic lupus erythematosus: fine mapping of Sles1 to less than 1 mb

Sle is a susceptibility locus for systemic autoimmunity derived from the lupus-prone NZM2410 mouse. The New Zealand White-derived suppressive modifier Sles1 was identified as a specific modifier of Sle1 and prevents the development of IgG anti-chromatin autoantibodies mediated by Sle1 on the C57BL/6 (B6) background. Fine mapping of Sles1 with truncated congenic intervals localizes it to a approximately 956-kb segment of mouse chromosome 17. Sles1 completely abrogates the development of activated T and B cell populations in B6.Sle1. Despite this suppression of the Sle1-mediated cell surface activation phenotypes, B6.Sle1 Sles1 splenic B cells still exhibit intrinsic ERK phosphorylation. Classic genetic complementation tests using the nonautoimmmune 129/SvJ mouse suggests that this strain possesses a Sles1 allele complementary to that of New Zealand White, as evidenced by the lack of glomerulonephritis, splenomegaly, and antinuclear autoantibody production seen in (129 x B6.Sle1 Sles1)F(1)s. These findings localize and characterize the suppressive properties of Sles1 and implicate 129 as a useful strain for aiding in the identification of this elusive epistatic modifier gene.

Immunisation with virion-loaded plasmacytoid or myeloid dendritic cells induces primary Th-1 immune responses

Dendritic cells (DCs) induce different types of immune responses depending on their lineage and activation signals. When exposed to inactivated pseudorabiesvirus (iPRV), plasmacytoid but not myeloid DCs released IFN-alpha and IL-12. Remarkably, both iPRV-pulsed DC types were able to induce primary IFN-gamma producing T cells and IgG isotype switching in vivo. In contrast, tetanus toxoid pulsed DCs did not induce detectable primary immune responses. The efficacy of antiviral T and B cell priming proved dependent on the recipient's genotype. We conclude that either plasmacytoid or myeloid DCs pulsed with inactivated virus suffice to induce primary Th1-polarised immune responses.

Identification of quantitative trait loci controlling cortical motor evoked potentials in experimental autoimmune encephalomyelitis: correlation with incidence, onset and severity of disease

Experimental autoimmune encephalomyelitis (EAE) is a polygenic chronic inflammatory demyelinating disease of the nervous system, commonly used as an animal model of multiple sclerosis. Previous studies have identified multiple quantitative trait loci (QTLs) controlling different aspects of disease pathogenesis. However, direct genetic control of cortical motor evoked potentials (cMEPs) as a straightforward measure of extent of demyelination or synaptic block has not been investigated earlier. Here, we examined the genetic control of different traits of EAE in a F2 intercross population generated from the EAE susceptible SJL/J (SJL) and the EAE resistant C57BL/10.S (B10.S) mouse strains involving 400 animals. The genotypes of 150 microsatellite markers were determined in each animal and correlated to phenotypic data of onset and severity of disease, cell infiltration and cMEPs. Nine QTLs were identified. Three sex-linked QTLs mapped to chromosomes 2, 10 and 18 linked to disease severity in females, whereas QTLs on chromosomes 1, 8 and 15 linked to the latency of the cMEPs. QTLs affecting T-lymphocyte, B-lymphocyte and microglia infiltration mapped on chromosomes 8 and 15. The cMEP-associated QTLs correlated with incidence, onset or severity of disease, e.g. QTL on chromosome 8, 32-48 cM (EAE 31) (LOD 6.9, P<0.001), associated to cMEP latencies in non-immunized mice and correlated with disease onset and EAE 32 on chromosome 15 linked to cMEP latencies 15 days post-immunization and correlated with disease severity. Additionally, applying tissue microarray technology, we identified QTLs associated to microglia and lymphocytes infiltration on chromosomes 8 and 15, which are different from the QTLs controlling cMEP latencies. There were no alterations in the morphological appearance of the myelin sheaths. Our findings suggest a possible role of myelin composition and/or synaptic transmission in susceptibility to EAE.

Cognate recognition of the endothelium induces HY-specific CD8+ T-lymphocyte transendothelial migration (diapedesis) in vivo

The physiologic significance of MHC-peptide complex presentation by endothelial cells (ECs) to trafficking T lymphocytes remains unresolved. On the basis of our observation that cognate recognition of ECs enhanced transendothelial migration of antigen-specific T lymphocytes in vitro, we have proposed that by displaying antigenic peptides from the underlying tissue, ECs promote the recruitment of antigen-specific T cells. In this study, we have tested this hypothesis by comparing the trafficking of HY-specific T lymphocytes into antigenic and nonantigenic tissue using in vivo models of T-cell recruitment. Up-regulated expression of H2 molecules presenting endogenous antigen in the peritoneal mesothelium and vessels led to the local recruitment of HY-specific T cells in male, but not female, mice. Intravital microscopy experiments analyzing EC–HY-specific T-cell interactions in the cremasteric vascular bed revealed that cognate recognition of the endothelium results in enhanced diapedesis of T cells into the tissue, while not affecting rolling and adhesion. Our results are consistent with the hypothesis that, under inflammatory conditions, antigen presentation by the endothelium contributes to the development and specificity of T-cell–mediated inflammation by favoring the selective migration of antigen-specific T cells. (Blood. 2004;103:3111-3116)

Role of ICAM-1 and P-selectin expression in the development and effector function of CD4+CD25+regulatory T cells

Dynamic regulatory mechanisms prevent autoreactive T cell activation. Upon T cell receptor crosslinking, CD4+CD25+ T regulatory (T(R)) cells block both the proliferation and cytokine production of CD4+CD25- effector cells in an apparent antigen non-specific manner. Within the T(R)population, L-selectin (CD62L)(hi)T(R)cells have been described as more efficient suppressors of T cell proliferation than CD62L(low)T(R)cells. We have previously reported that CD4+CD25+CD62L(hi)T(R)cells express elevated levels of two additional adhesion molecules, ICAM-1 (CD54) and P-selectin (CD62P) in comparison to non-T(R)cells. In the current study, we investigated the functional contribution of CD54 and CD62P expression to the suppressive phenotype of T(R)cells both in vitro and in vivo. While the CD4+CD25+ T(R)cell population was demonstrated to be significantly larger in CD62P-/- mice than in wild-type C57BL/6 mice, CD62P-/- T(R)cell function was deficient in vitro, but not in vivo. Interestingly, we detected no deficiencies in T(R)cell numbers or effector function in CD54-/- mice suggesting that T(R)cells may differ from effector CD4+ T cells in the requirement for CD54 expression within the immunological synapse. Collectively, these findings indicate that CD62P may influence T(R)cell differentiation/development and that T(R)cell activation occurs independently of CD54 expression.

Are major histocompatibility complex molecules involved in the survival of naive CD4+ T cells?

The exact role of major histocompatibility complex (MHC) molecules in the peripheral survival of naive T cells is controversial, as some studies have suggested that they are critically required whereas others have suggested that they are not. Here we controlled for some of the features that differed among the earlier studies, and analyzed both the survival and expansion of naive CD4⁺ T cells transferred into MHC syngeneic, allogeneic, or MHC negative environments. We found that naive T cells transferred into MHC negative or allogeneic environments often fail to survive because of rejection and/or competition by natural killer (NK) cells, rather than failure to recognize a particular MHC allele. In the absence of NK cells, naive CD4⁺ T cells survived equally well regardless of the MHC type of the host. There was, however, an MHC requirement for extensive space-induced “homeostatic” expansion. Although the first few divisions occurred in the absence of MHC molecules, the cells did not continue to divide or transit to a CD44^hi phenotype. Surprisingly, this MHC requirement could be satisfied by alleles other than the restricting haplotype. Therefore, space-induced expansion and survival are two different phenomena displaying different MHC requirements. Memory CD4⁺ T cells, whose survival and expansion showed no requirements for MHC molecules at all, dampened the space-induced expansion of naive cells, showing that the two populations are not independent in their requirements for peripheral niches.

In vivo immunogenetics: from MIC to RAET1 loci

The major histocompatibility complex (MHC) comprises approximately one thousandth of the genome and encompasses its most polymorphic members. This diversity enables the MHC, at the population level, to counteract the extraordinarily diverse microbiological threats. Reviewed here are two separate sets of MHC class I genes: MIC and RAET1. Whilst the former are encoded within the MHC (6p21.3), the latter are located on the opposite arm of the same chromosome (6q24.2-q25.3). Differing from the prototypical class I genes in structure, transcription, diversity and potential function, they both exemplify the versatility of the MHC fold, despite convergence onto a single ligand, the activatory C-type lectin-like receptor, NKG2D. Why the immune system uses two distinct gene families to interact with a unique ligand remains a fascinating question. To answer this question, the reader will be chronologically exposed to the field whilst following a single thread, i.e. genomics and gene diversity.

A novel locus affecting serum levels of IgG2a maps to the murine H2 region

The effects of genes in the murine H2 region on basal immunoglobulin levels were investigated and ratios of IgG1/IgG2a were calculated, as low ratios indicate a Th1 cytokine mileu. H2b mice with B10 or BALB genetic backgrounds had higher levels of IgG2a than H2k and H2d congenic strains, and hence had low IgG1/IgG2a ratios. B10 (H2b) mice generally had high levels of IgG2b, IgG3, IgA and IgM, but this outcome was more variable. The high IgG2a phenotype was denoted Igis1 (Immunoglobulin isotype-1) and mapped telomeric of IEbeta using B10.A(4R) mice (high IgG2a) and B10.A(3R) and B10.A(5R) mice (low IgG2a). Further mapping in B10.A(2R), B10.A(1R) and B10.A(18R) mice placed Igis1 in the 27kb region between G7c and G7e.

Cutting Edge: Alloimmune Responses Against Major and Minor Histocompatibility Antigens: Distinct Division Kinetics and Requirement for CD28 Costimulation

Comparative study of alloimmune responses against major and minor histocompatibility Ags has been limited by the lack of suitable assays. Here, we use a bioassay that permits tracking of alloreactive CD4+ T cell populations as they proliferate in response to major or minor histocompatibility Ags in vivo. Division of alloreactive CD4+ T cells proceeded more rapidly in response to major histocompatibility Ags than minor Ags, although CD4+ T cells alloreactive to minor Ags had a similar capacity to divide successively up to eight times after stimulation. Allorecognition of minor histocompatibility Ags was highly dependent on CD28 costimulation, with the frequency of CD4+ T cells proliferating in response to minor Ags in the absence of CD28 costimulation reduced up to 20-fold. These findings highlight differences in signaling processes that lead to allorecognition of major and minor histocompatibility Ags and have implications on the design of interventions aimed at abrogating these responses.

Major histocompatibility complex (MHC) class I KbDb -/- deficient mice possess functional CD8+ T cells and natural killer cells

We obtained mice deficient for major histocompatibility complex (MHC) molecules encoded by the H-2K and H-2D genes. H-2 KbDb -/- mice express no detectable classical MHC class I-region associated (Ia) heavy chains, although beta2-microglobulin and the nonclassical class Ib proteins examined are expressed normally. KbDb -/- mice have greatly reduced numbers of mature CD8+ T cells, indicating that selection of the vast majority (>90%) of CD8+ T cells cannot be compensated for by beta2-microglobulin-associated molecules other than classical H-2K and D locus products. In accord with the greatly reduced number of CD8+ T cells, spleen cells from KbDb -/- mice do not generate cytotoxic responses in primary mixed-lymphocyte cultures against MHC-disparate (allogeneic) cells. However, in vivo priming of KbDb -/- mice with allogeneic cells resulted in strong CD8+ MHC class Ia-specific allogeneic responses. Thus, a minor population of functionally competent peripheral CD8+ T cells capable of strong cytotoxic activity arises in the complete absence of classical MHC class Ia molecules. KbDb -/- animals also have natural killer cells that retain their cytotoxic potential.

T-cell and major histocompatibility complex requirements for obliterative airway disease in heterotopically transplanted murine tracheas

BACKGROUND

One third of human lung allografts develop chronic rejection manifested as obliterative bronchiolitis. Heterotopically transplanted allogeneic murine tracheas develop obliterative airway disease (OAD) leading to a lesion resembling human obliterative bronchiolitis. The purpose of this study was to determine the T-cell and major histocompatibility complex (MHC) molecule requirements of murine OAD.

METHODS

BALB/c allografts and C57BL/6 (B6) isografts were transplanted into B6 severe combined immunodeficient (SCID) and B6 wild-type (WT) recipients. MHC class I-discrepant bm1 grafts, class II-discrepant bm12 grafts, and F1(bm1 x bm12) (F1) grafts also were transplanted into B6 WT recipients. Grafts were harvested between days 5 and 56 following transplantation and evaluated histologically.

RESULTS

Complete MHC-disparate allografts placed in WT recipients had significantly more disease than similar allografts in SCID recipients, and the latter were indistinguishable from isografts in either WT or SCID recipients, indicating a lymphocyte dependence on the disease development. Pathology was significantly more severe in bm1 and F1 allografts than in isografts recovered from B6 recipients, but bm12 allografts appeared no different than isografts. T-cell infiltrates in these bm12 allografts contained only CD4+ cells, whereas infiltrates in the BALB/c, bm1, and F1 allografts manifesting OAD contained both CD4+ and CD8+ cells. No grafts had significant B-cell infiltration.

CONCLUSIONS

These findings suggest that OAD relies on a host T-cell response that includes CD8+ cells, directed against allo-class I-bearing donor cells within the graft.

New Genetic Loci That Control Susceptibility and Symptoms of Experimental Allergic Encephalomyelitis in Inbred Mice

Experimental allergic encephalomyelitis (EAE), the principal animal model of multiple sclerosis, is a genetically determined phenotype. In this study, analyses of the cumulative disease frequencies in parental, F1 hybrid, and F2 mice, derived from the EAE-susceptible SJL/J strain and the EAE-resistant B10.S/DvTe strain, confirmed that susceptibility to EAE is not inherited as a simple Mendelian trait. Whole genome scanning, using 150 informative microsatellite markers and a panel of 291 affected and 390 unaffected F2 progeny, revealed significant linkage of EAE susceptibility to marker loci on chromosomes 7 (eae4) and 17, distal to H2 (eae5). Quantitative trait loci for EAE severity, duration, and onset were identified on chromosomes 11 (eae6, and eae7), 2 (eae8), 9 (eae9), and 3 (eae10). While each locus reported in this study is important in susceptibility or disease course, interactions between marker loci were not statistically significant in models of genetic control. One locus, eae7, colocalizes to the same region of chromosome 11 as Orch3 and Idd4, susceptibility loci in autoimmune orchitis and insulin-dependent diabetes mellitus, respectively. Importantly, eae5 and eae7 are syntenic with human chromosomes 6p21 and 17q22, respectively, two regions of potential significance recently identified in human multiple sclerosis genome scans.

IL-12 Modulates Expression of Hypersensitivity Pneumonitis

Hypersensitivity pneumonitis (HP) is a granulomatous, inflammatory lung disease caused by inhalation of organic Ags, most commonly thermophilic actinomycetes. Only a minority of individuals exposed to these Ags develops disease, suggesting that host factors are important for the expression of HP. We compared the expression of HP in a sensitive strain of mice, C57BL/6, and in a resistant strain of mice, DBA/2. They were exposed to the thermophilic bacteria Saccharopolyspora rectivirgula (SR) or to saline alone for 3 consecutive days/week for 3 wk. After exposure to Ag, C57BL/6 mice, but not DBA/2 mice, developed granulomatous inflammation with an increase in lung index (lung weight). Both strains had similar amounts of Ag delivered to the lungs after intranasal installation, as determined with 14C-labeled Ag. Both also had similar increases in total bronchoalveolar cells after Ag exposure, but the C57BL/6 mice had more lymphocytes. Compared with the resistant strain, the sensitive strain had a significantly greater Ag-induced increase in IL-12 and IFN-γ gene expression. DBA/2 mice resembled sensitive, C57BL/6 mice if they received IL-12 augmentation therapy at the time of Ag exposure. These findings were not limited to lung, since both unstimulated and SR-stimulated spleen cells from C57BL/6 mice released significantly more IL-12 than cells from DBA/2 mice. However, spleen cells from DBA/2 mice made more IFN-γ when exposed to IL-12, than cells from C57BL/6 mice. These results suggest that the IL-12 response to Ag may modulate in part the expression of HP.

A microsatellite-based MHC genotyping system for house mice (Mus domesticus)

Major histocompatibility complex (MHC) genes are the most polymorphic loci known for vertebrates. Although this has been known for over two decades, the selective forces maintaining this genetic diversity are unclear. Efforts to study selection on these loci in nature have been hampered because no simple MHC typing systems are available. Here, we describe and evaluate a microsatellite-based MHC genotyping system for house mice (Mus domesticus). Thirty-five MHC-linked microsatellite loci were tested for amplification and scoring reliability, and 21 were deemed useful. These 21 loci were efficient at discriminating among nine serologically distinct MHC haplotypes, with 52% of microsatellite pairs providing 100% resolution. Since these microsatellite loci are scattered across the entire MHC region, they will be effective at detecting recombinant haplotypes. The number of alleles is higher for microsatellites inside the MHC than outside it, which presumably reflects genetic hitchhiking with MHC alleles under balancing selection. This microsatellite typing system now allows testing hypotheses about the nature of selection operating on MHC genes in natural populations of M. domesticus and other murid rodent species.

T-Cell epitope mapping the PorB protein of serogroup B Neisseria meningitidis in B10 congenic strains of mice

T-cell epitope mapping the meningococcal serotype 15 PorB protein performed in this study in three congenic strains of mice with B10 genetic background revealed at least three murine T-cell epitopes (55-72, 163-180, and 226-261), located in the highly conserved putative transmembrane regions of Neisserial porins. Proliferation assays with popliteal lymph node cells derived from mice immunized with the PorB protein or with synthetic 18-mer peptides showed that epitope 163-180 immunized only in the H-2d haplotype, epitope 55-72 could be presented by both H-2f and H-2s molecules, while the 226-261 region covered by three overlapping peptides could be efficiently recognized in context of all three MHC class II haplotypes studied. Inhibition experiments with blocking I-Aalpha- and I-Ealpha-specific mAb showed that peptide 163-180 was presented by I-Ad and peptide 244-261 was presented by both I-Af and I-As. In addition, evidence was obtained that peptide 226-243 was presented in context of H-2d or I-As haplotypes and peptide 55-72 was presented in context of I-Af and I-As loci. Finally, the Norwegian outer membrane vesicle vaccine, but not the purified PorB protein, could recall responses in mice immunized with synthetic peptides corresponding to the 226-261 region. Altogether, these results suggest that T-cell epitopes identified on the serotype 15 PorB protein, particularly those presented by several MHC class II molecules (e.g., 226-261), could have important implications for the development of meningococcal vaccines.

Hypothesis: MHC class I, rather than just a flagpole for CD8+ T cells is also a protease in its own right

Ever since the discovery of MHC class I restriction and the onslaught of the dual receptor hypothesis, MHC class I has been perceived as a passive entity in TCR recognition and the appropriate antigen processing and presentation pathways. However, numerous experimental observations and theoretical considerations are difficult or unable to be explained by the accepted mechanism of class I antigen presentation. Proteases within and outside the endoplasmic reticulum (ER) are evoked to be solely responsible for the generation of the appropriate 8-10 amino acid-long peptides associated with MHC class I. A MHC class I with site-restricted ER protease activity would overcome most of the present difficulties in explaining MHC class I antigen presentation.

Genetic predisposition to lymphomas in mice

The spontaneous mouse lymphoma is a model of multifactorial genetic disease. It is induced by the endogenous murine leukemia virus (MuLV), whose genome is inherited as a Mendelian dominant trait. Lymphoma development takes place in multiple stages affected by many host genetic and epigenetic factors. An inbred strain SL/Kh with a high incidence of pre-B lymphomas has been established and the genetic predisposition of SL/Kh mice to lymphomas is being studied in the crosses with other inbred strains of mice. In the cross to the NFS/N lacking endogenous MuLV genome, it has been shown that lymphomas are induced by the expression of Emv-11 provirus (Chr. 7), and the types of B-lineage lymphomas are determined by combinations of the host genes, Esl-1 (Chr. 17) and Foc-1 (Chr. 4). Another gene, Tlsm-1 (Chr. 7) that determines the type of lymphomas to be T-lineage, is identified in the cross with AKR/Ms, with a high incidence of T-lymphomas. The role of the thymus in the development of T-lymphomas in the mouse, and the possible relevance of Tlsm-1 in this step, is discussed. The length of the latent period is determined by a gene Lia-1 (Chr. 17). A maternal resistance factor that is a maternal antibody to MuLV transmitted via milk and that epigenetically inhibits MuLV expression in SL/Ni-Eco-, one of subline of SL/NI mice, has been shown. Weak but definitive maternal resistance also operates in SL/Ni-Eco+, a subline lacking the maternal antibody to MuLV. In the latter, there is a recessive resistance gene Nir-1 (Chr. 4). In the cross with MSM/Ms, a wild mice-derived inbred strain, two resistance genes, Msmr-1 (Chr. 17) and Msmr-2 (Chr. 18), have been identified. In SL/Kh, all of these host genetic and epigenetic factors are favorable for lymphoma development. This model offers not only an understanding of the pathogenesis of virus-induced lymphomas but also may provide starting material for the comparative approach to homologous human diseases.

Typing of murine major histocompatibility complex with a microsatellite in the class II Eb gene

Two DNA-based assays were developed for identification of the H2 alleles present in the 12 standard mouse MHC haplotypes H2b, H2d, H2f, H2j, H2k, H2p, H2q, H2r, H2s, H2u, H2v and H2z. The assays utilized polymerase chain reaction (PCR) amplification of a short stretch of genomic DNA including a highly polymorphic microsatellite from the second intron of the class II Eb gene within the murine major histocompatibility complex. The H2 Eb alleles were discerned by restriction fragment length polymorphism (RFLP) and heteroduplex analyses. For RFLP analysis amplified DNAs were digested with the restriction endonuclease Fnu4HI which delineated seven of the 12 alleles. A distinct pattern was obtained for the haplotypes H2d, H2j, H2k and H2p, whereas a group specific but distinct pattern was obtained for each of the three groups H2b, H2r and H2v, H2f, H2q and H2s, H2u and H2z. Heteroduplex analysis using a pair of haplotypes at a time helped further discriminate H2q from H2f or H2s. More importantly, heteroduplexing was quite informative in delineating the identity or disparity between two given haplotypes in a single step of PCR amplification. Both the RFLP and heteroduplex analyses are extremely sensitive and simple to operate, and since the target is genomic DNA, they can be carried out using any cell or tissue type.

Determination of T cell epitopes with random peptide libraries

A new approach to T cell epitope determination is presented. Critical amino acids for the induction of cytotoxic T cell responses were identified using synthetic peptide libraries with single defined sequence positions combined with randomized sequence positions. Sequences for potential T cell epitopes were deduced from scan profiles using combinations of the active amino acids. Highly potent epitopes for cytotoxic T lymphocytes were obtained. Epitopes defined by this approach are, as shown in this communication, not necessarily the natural epitopes and, therefore, were named synthetic epitopes. They can serve effectively for the development of vaccines or for the determination of T cell receptor antagonists.

Emergence in C kappa knockout mice of a diverse cytotoxic T lymphocyte repertoire that recognizes a single peptide from the immunoglobulin constant kappa light chain region

Allotype- or idiotype-specific CD4+ T cells have been reported to recognize immunoglobulin (Ig) peptides presented by class II molecules. In contrast, few data are available concerning the generation of Ig peptide-specific CD8+ T cells. We have therefore investigated whether T-depleted spleen cells from Ig kappa light chain-expressing 129/Sv mice (129 kappa +/+) could induce, in C kappa knockout mice (129 kappa -/-), the generation of Ig constant kappa light chain region (C kappa)-specific cytotoxic T lymphocytes (CTL). The determination of TCR beta chain expressed by nine CTL clones, together with the use of a library of overlapping peptides spanning the whole C kappa sequence, show that the B cells from kappa +/+ mice are able to elicit in C kappa knockout mice, the emergence of a diverse CTL repertoire that recognizes one single C kappa peptide presented by the H-2Kb class I molecule. In addition, these data support the notion that B cells are able to process and present on their class I molecules, peptides generated from their own kappa light chains.

Mouse H2 congenic intervals: analysis and use for mapping

In this study we exploit the unique genetic resource of inbred mouse major histocompatibility complex (H2) congenic and recombinant strains to construct a high-resolution map of microsatellite loci in and around the H2 region, as well as an independent genetic map of other loci on mouse Chromosome (Chr) 17. Microsatellite loci were analyzed in 11 C57BL/10 (B10) strains to determine the size of the congenic interval in each. The length of the congenic interval found in each strain varied widely. Interestingly, the intervals were generally smaller than statistical expectations. However, the observed congenic intervals were still sufficiently long that these strains and probably wild-derived H2 congenics are an important source of genetic variability. The staggered ends of the various congenic intervals and the recombinants were used to construct the map. This map will be useful for physical cloning and to help localize novel genes. As evidence of the mapping application of congenic strains, locational information was derived about Trp53-ps and Stl.

Vascular cell adhesion molecule-1 is induced on vascular endothelia and medial smooth muscle cells in experimental cardiac allograft vasculopathy

BACKGROUND

Cardiac allograft vasculopathy (CAV) is the major cause of late death among heart transplant recipients. The pathogenesis of CAV is poorly understood.

METHODS AND RESULTS

To better characterize CAV, we performed immunohistochemical analysis of vascular lesions in a previously described murine model of CAV. The B10.A strain hearts were transplanted heterotopically into B10.BR strain recipients. The cardiac allografts were harvested from 1 to 2 months after implantation. The majority of epicardial and intramyocardial coronary arteries in explanted hearts had developed intimal thickening. The cellular infiltrate of the intimal thickening, major histocompatibility (MHC) antigens, intracellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) expression were studied with the use of immunohistochemistry. In experimental CAV in mice, the cellular infiltrate of expanded intima consisted of macrophages, T lymphocytes, and smooth muscle cells. A substantial number of macrophages and T lymphocytes within the expanded intima expressed MHC class II antigen, a marker of cellular activation. The vessel wall cells also appeared to be activated due to their expression of endothelium-leukocyte adhesion molecules. The vascular endothelium of cardiac allografts displayed ICAM-1, VCAM-1, and unmatched MHC antigen (MHC class I in this model) upregulation. The medial smooth muscle cells also expressed VCAM-1 and unmatched MHC antigen.

CONCLUSIONS

These findings suggest that (1) the cellular infiltrate of the expanded intima in experimental CAV is similar to that of human CAV, (2) experimental CAV is a local immune-mediated process requiring active participation of donor vessel wall cells and recipient mononuclear cells, and (3) coexpression of adhesion molecules and unmatched MHC antigen identifies endothelial cells as immune targets for activated host mononuclear cells. Furthermore, the presence of both VCAM-1 and unmatched MHC antigen supports a central role for medial smooth muscle cells as allogeneic immune stimulator.

Immune response to hepatitis C virus core protein in mice

To analyse the immune response to the hepatitis C virus (HCV) core protein, we immunized mice with the protein. BALB/c (H-2d) and C3H/He (H-2k) mice were high responders, while C57BL/6 (H-2b) mice were low responders in terms of Th cell proliferative responses. All the strains showed comparable levels of antibody responses to the HCV core protein. The Th cell lines recognized residues 61-90 of the HCV core protein in the context of I-Ad (BALB/c) and residues 11-30 in the context of I-Ek (C3H/He), respectively. The Th cell lines were restricted by I-Ab in C57BL/6 mice but recognized no synthetic peptide that spanned the region, although derivative clones from the line recognized residues 1-20 and 91-110 of the HCV core protein, respectively. The Th cell lines were Th 1 subset in all three strains based on the profile of lymphokine secretion. The major B cell epitope of the protein was found to be within residues 21-40 of the HCV core protein in all three strains. These observations should be useful for better understanding of the immune response to the HCV core protein in vivo.

Prevention of atherosclerosis in apolipoprotein E-deficient mice by bone marrow transplantation

Apolipoprotein E (apoE) deficiency causes severe hyperlipidemia and atherosclerosis in humans and in gene-targeted mice. Although the majority of apoE in plasma is of hepatic origin, apoE is synthesized by a variety of cell types, including macrophages. Because macrophages derive from hematopoietic cells, bone marrow transplantation was used to examine the potential of apoE synthesized by bone marrow-derived cells to correct the hyperlipidemia and atherosclerosis caused by apoE deficiency. After transplantation of bone marrow from mice with the normal apoE gene into apoE-deficient mice, apoE was detected in serum and promoted clearance of lipoproteins and normalization of serum cholesterol levels. ApoE-deficient mice given transplants of normal bone marrow showed virtually complete protection from diet-induced atherosclerosis.

On the cellular basis of immunological T cell memory

We have studied memory in T cell receptor (TCR) transgenic mice expressing a Db-restricted TCR specific for the male peptide (H-Y). CD8+ T cells from female TCR transgenic C57BL/6 (B6) mice were activated by transferring them into X-irradiated male (B6 x bm12)F1 hybrid recipients. Subsequently, they were highly purified by cell sorting and transferred for various lengths of time into female B6 nu/nu recipient mice. Other nu/nu recipient mice received highly purified naive T cells expressing the transgenic TCR. The functional potential of naive and "memory" T cells was analyzed by stimulation with male cells in vivo. The results show that memory cells can be derived from activated T cells and persist in the absence of antigen for at least 13 weeks. Naive and memory T cells differ in that memory T cells give a more vigorous and sustained response than naive T cells.

MtDNA-encoded histocompatibility antigens

Mitochondrially encoded H antigens are by-products of a system that has evolved in vertebrates to present peptides from intracellular pathogens on the cell surface for detection by CTLs, which can lyse the infected cell. CTL lines and clones with defined specificity against mitochondrial H antigens, which can be maintained in culture for long periods, offer a unique tool in mitochondrial genetics. Expression of polymorphic mitochondrial H antigens depends on both the presence and the activity of the corresponding mitochondrial genome, and CTLs can provide strong selection against cells displaying their cognate antigen.

Thymic selection of CD8+ single positive cells with a class II major histocompatibility complex-restricted receptor

We describe mice that express a transgenic T cell receptor alpha/beta (TCR-alpha/beta) specific for peptide 111-119 from influenza hemagglutinin presented by I-Ed class II major histocompatibility complex (MHC) molecules. The transgenic TCR is expressed on CD4+8- as well as CD4-8+ mature T cells even in mice that are deficient in rearrangement or do not express endogenous TCR-alpha genes. The CD4-8+ T cells require I-Ed class II MHC molecules for positive selection and can be activated to proliferate and to kill by I-Ed molecules presenting the relevant peptide. Full maturation of these cells, however, also requires the presence of class I MHC molecules. The results are compatible with the notion that T cell maturation requires multiple receptor-ligand interactions and establish an exception to the rule that class II-restricted TCRs are exclusively expressed by mature CD4+8- cells.

Antigenic heterogeneity of Qa-2 antigens in C57BL/6

The Qa-2 antigens are class I-like molecules encoded by genes mapped telomeric to the H-2D region on chromosome 17 in the mouse. A panel of 8 new monoclonal anti-Qa-2 antibodies derived from a C3H.KBR anti-C3H. SW immunization was studied. Immunoprecipitation of 125I-labeled C57BL/6 splenocyte antigens showed that all of these antibodies precipitated 40 kDa molecules which could be completely precleared by the monoclonal antibody 20-8-4, which had previously been shown to crossreact with Qa-2. One of the monoclonal antibodies (1-12-1), however, was found not to completely preclear Qa-2 antigens precipitable by the other 7 antibodies or by 20-8-4, suggesting the existence of at least two different species of Qa-2 molecules. Cell lines transfected with Q7 or Q9 genes were reactive with all 9 antibodies and the Qa-2 antigens expressed on surface membranes of these cells were completely precleared by both 20-8-4 and 1-12-1. Therefore, the observed heterogeneity of these molecules cannot be explained by an antigenic difference between the Q7 and Q9 gene products. 2D gel analyses showed identical pI spectra between Qa-2 molecules precipitated with 20-8-4 and 1-12-1. In addition, all of the monoclonal antibodies reacted with labeled antigen preparations following treatment with Endo F or neuraminidase, indicating that carbohydrate moieties are probably not responsible for the antigenic difference between the two species of Qa-2 antigen.

CD4+8- help prevents rapid deletion of CD8+ cells after a transient response to antigen

We have followed the fate of mature CD8+ T cells with a male-specific transgenic T cell receptor after antigenic stimulation with hemopoietic cells in the absence or presence of help. Our data show that mature CD8+ T cells can be deleted after a 3-week period of transient activation and that help, e.g. in the form of interleukin-2, can considerably delay the deletion. These experiments have implications for the design of protocols aiming at the establishment of specific immunological tolerance in T cells.

Allogeneic recognition of class I molecules: anti-H-2Ld repertoire of H-2b mice includes T cells recognizing mutant class II H-2b (Abm12) molecules

Two major histocompatibility complex (MHC) class I-reactive T cell clones derived from H-2b mice, generated against the allogeneic Ld molecule, were found to recognize the H-2b class II mutant Abm12 molecule as well. In addition, these clones also recognize the class II A(s) molecule, and display a class II-dependent reactivity to staphylococcal enterotoxin B. Neither the class I nor the class II alloreactivities of the clones were found to be dependent on other MHC molecules. Both clones express CD4+CD8- phenotypes. The CD4 molecule appears to be involved in their class II reactivity, while little or no role for CD4 could be detected in the class I reactivity. This is the first report of a class I/class II cross-reactivity being mediated by CD4+ T cells. The structural basis for this cross-reactivity is discussed.

Pancreatic beta-cell destruction in non-obese diabetic mice

We determined the natural history of the widespread pancreatic islet beta-cell destruction that precedes the onset of spontaneous putative autoimmune diabetes mellitus in NOD mice. For this purpose, we performed both histological and immunocytochemical examinations of pancreata retrieved from mice at 2 through 30 weeks of age. An overexpression of la antigens was identified on islet beta cells at 4 weeks of age, without evidence of mononuclear cell infiltration. The abnormal expression of la antigens was age-related and was associated with hyperexpression of class I antigens and progressive islet cell histologic damage after 17 weeks of age. Immunocytochemical examination of islet cell infiltrate showed that the number of macrophages did not increase during the early phase of islet cell damage in these mice. The L3T4/Lyt-2 ratio increased after 7 weeks of age, but was 1:1 in the late stage of insulitis. These findings suggest that widespread islet beta-cell destruction is a process that begins primarily with derangements of the pancreatic beta-cell immune pattern, which may trigger a mononuclear cell reaction.

Leishmania major-specific, CD4+, major histocompatibility complex class II-restricted T cells derived in vitro from lymphoid tissues of naive mice

Several studies indicate that the outcome of experimental murine cutaneous leishmaniasis caused by Leishmania major (Lm) is determined by immunological events occurring shortly after infection. These events lead to outgrowth of either protective CD4+ T cells in the C57BL/6 mouse, which cures, or exacerbative cells in the BALB/c mouse, which succumbs to disease. Potential factors influencing the outgrowth of protective or exacerbative T cells include antigen-presenting cells (APC), cytokines, and parasite antigens. An in vitro system, in which one could precisely control the factors shaping early events in the T cell response to Lm, would be very useful. To this end, we have examined the in vitro response of naive lymphocytes to Lm promastigotes. The data presented here show that Lm-specific CD4+ T cell receptor alpha/beta + T cells can be generated in vitro from spleen and lymph node cell populations of naive mice. Furthermore, they can be obtained from the CD44low (unprimed) population of T lymphocytes, indicating that in vitro priming occurs. The ability to generate these T cells is dependent on the presence of live parasites and is not due to a parasite-derived nonspecific T cell mitogen. Restimulation, as assayed by proliferation, requires APC bearing syngeneic I-A. Optimal restimulation of the in vitro derived T cells is achieved only when live promastigotes are used. The T cells do not proliferate in response to a frozen-and-thawed lysate of promastigotes, yet they exhibit mild reactivity to lysates prepared from heat-shocked promastigotes. Furthermore, they do not recognize two predominant antigens on the promastigote surface, lipophosphoglycan and gp63. T cells derived in vitro with Lm show crossreactivity with live L. donovani, less crossreactivity with live L. mexicana, and no crossreactivity with live Bacillus-Calmette-Guerin or live Brugia malayi microfilariae. Finally, these early T cells, whether derived from healing C57BL/6 or nonhealing BALB/c mice, produce interleukin 2 (IL-2), IL-4, and interferon gamma.

A highly polymorphic microsatellite in the class II Eb gene allows tracing of major histocompatibility complex evolution in mouse

A hallmark of major histocompatibility complex (MHC) genes is their extraordinarily high level of polymorphism. Polymorphic residues on MHC molecules determine which peptide ligands they bind and present to effector T lymphocytes. Although the genetic mechanisms responsible for MHC polymorphism have been delineated, the timetable and the pathway of their diversification remain unclear. To trace MHC evolution, we have characterized a highly polymorphic microsatellite containing tandem repeats (TRs) of two tetranucleotide units, TGGA and GGCA, located at the 3' end of the second intron in the class II Eb gene of mouse. On the basis of length as well as sequence variations, 11 TR alleles were defined in 55 inbred mouse strains, which included MHC recombinant haplotypes and haplotypes derived from different subspecies of mouse. In this extensive sampling, a striking concordance was observed between the serologically identified class II proteins and the associated TR alleles. Examination of several strains carrying the same MHC haplotypes as well as strains carrying recombinant MHC haplotypes indicates that TR alleles are extremely stable. These observations suggest that TR polymorphism predates the separation of various subspecies of mouse. On the basis of sequence divergence, a genealogical tree has been constructed to depict evolution of the different TR alleles. Finally, evidence is presented that suggests this microsatellite polymorphism is generated by slipped-strand mispairing during DNA replication.

Cross-reactivity among evolutionarily distant major histocompatibility complex class I molecules (HLA-B27 and H-2Kk) revealed by xenoreactive T lymphocytes

A set of mouse HLA-B27-reactive cytotoxic T lymphocyte clones were found to recognize the HLA-B27 molecule in an H-2-unrestricted manner, i.e. independently of any mouse major histocompatibility complex (MHC) molecule. The reactivity patterns of these clones on HLA-B27 variants (positive only on HLA-B*2702 and HLA-B*2701) allowed the identification of residues N77 and A81 of the HLA-B27 molecule as important for their reactivity. The location of these residues in the peptide-binding groove (specificity pocket F) suggested that the reactivity of the clones is dependent on HLA-B27-bound peptide(s). However, several other class I molecules sharing these residues (N77 and A81) were not recognized, indicating that other residues might also be involved. One of the clones was found to display an interesting cross-reactivity with allogeneic H-2Kk molecules, sharing N77 and A81 with HLA-B*2702. Sequence comparison suggested the involvement of residue H9, located in specificity pocket B of the peptide-binding groove, and revealed some similarity of pockets B in HLA-B27 and H-2Kk. The structural basis of such T cell-mediated MHC cross-reactions across species barriers is discussed.

Characterization of a V kappa family in Mus musculus castaneus: expansion at the subset level

We have examined the same kappa chain variable (V kappa) region family in several mouse species in order to observe short-term, incremental change at immunoglobulin (Ig) multigene loci. In the present study, the Igk-V24 family has been characterized in a Mus m. castaneus colony derived from individuals originating in Thailand and compared to the same family in Mus m. domesticus (BALB/c) and Mus pahari, representing about 1-2 and about 5-9 million years of evolution, respectively. Southern hybridization of genomic DNA with a probe encoding the prototype Igk-V24 coding region reveals restriction fragment patterns indicative of two distinct M. m. castaneus haplotypes. These haplotypes appear to result from an unequal recombination between similar gene arrays, as their restriction patterns are unique but contain many common fragments. The complexity of these patterns indicates a marked expansion in the Igk-V24 family of M. m. castaneus relative to BALB/c and M. pahari. Additional analyses using probes specific for individual subsets demonstrate that the expansion is not general throughout the entire family, but is restricted to particular subsets and therefore to relatively short chromosomal segments. One subset alone accounts for most of the expansion and comprises over 40% of the entire M. m. castaneus family. The wide range of Igk-V24 family complexity seen among M. m. castaneus, M. m. domesticus, and M. pahari, as well as among the different M. m. castaneus family subsets, suggests a model of random evolution in V kappa family copy number rather than one which is selective.