Differential responsiveness to MIs locus antigens in graft-versus-host and host-versus-graft reactions

After (semi)allogeneic transplantation of lymphoid cells into lethally irradiated mice, the development of anti-host directed T effector cells can be demonstrated by means of a simple delayed-type hypersensitivity (DTH) assay. Using this assay we have shown that in H-2 compatible combinations Mls locus antigens can induce the generation of such T effector cells during a graft-versus-host (GvH) reaction. Other non-H-2 alloantigens are probably of minor importance. The capacity of Mls locus antigens to induce distinct anti-host DTH reactivity correlated with the capacity to induce a one-way mixed lymphocyte culture (MLC) response. Mls^a and Mls^c locus antigens initiated a positive MLC response as well as distinct GvH-related DTH reactivity. On the other hand, in the combination DBA/2 versus (BALB/c × DBA/2) F₁, the Mls^b locus antigen was not able to initiate in vitro proliferation, a lack of response which coincided with a marginal and short-lasting GvH-related DTH reactivity. In contrast, the host-versus-graft (HvG) DTH reaction of BALB/c and DBA/2 mice to subcutaneously injected (BALB/c × DBA/2) F₁ spleen cells was equally strong. Here antigens other than those coded for by the Mls locus were mainly responsible for the antigraft DTH response. These results suggest that T effector cells generated in GvH and HvG reactions are specific for largely different sets of minor histocompatibility antigens, with a selective stimulation by Mls locus antigens under GvH conditions.     

The expression of Mls c determinants on Mls a,Mls b,and Mls x prototypic strains

In the mouse sytem, specific determinants other than major histocompatibility complex (MHC) gene products are capable of inducing strong primary proliferative responses in naive T cells. These determinants are encoded by at least two gene loci designated as minor lymphocyte stimulatory (Mls) loci. In order to elucidate the biological role of the Mls system, an effort has been initiated to clarify the fundamental immunogenetic characteristics of the Mls system. In this report, we describe the unexpected finding that Mls ^c determinants are expressed on splenocytes of strains including those which have been used as prototypic examples of three other Mls types: Mls ^a (DBA/2, DBA/1), Mls ^b , (BALB/c), and Mls ^x (PL/J). The expression of Mls ^c by these strains was demonstrated both by the response patterns of unprimed T cells from MHC-identical inbred or F₁ hybrid strains and by the responses of a panel of Mls-specific T-cell clones. The experimental results reported here also suggest that the expression of Mls determinants may be influenced by multiple other genes, including MHC-linked genes.Abbreviations used in this paper MHC major histocompatibility complex - MLR mixed lymphocyte reaction - Mls minor lymphocyte stimulating locus antigen - MMC mitomycin C - NNT nylon wool nonadherent T cells     

Genetic analysis of the Mls system. Formal Mls typing of the commonly used inbred strains

In order to elucidate the biological role of minor lymphocyte stimulating (Mls) gene products, we have been investigating the fundamental immunogenetic characteristics of the Mls system. In this report, describe the distribution of stimulatory Mls products, Mls^a and Mls^c, in a panel of laboratory inbred strains based on the response pattern of H-2-compatible naive T-cell populations as well as monospecific Mls^a- or Mls^c-reactive T-cell clones. In addition, the expression of four different T-cell receptor (Tcr) b-V segment Tcrb-V3, –V6, –V8.1, and –V9, which were recently reported to be associated with T-cell recognition of Mls gene products in these strains, was examined. The results indicate that the majority of commonly used laboratory strains including those originally typed as Mls ^aare also expressing Mls^c determinants and that very few independent inbred strains are non-Mls ^c. Moreover, the pattern of Tcrb-V expression in spleen as well as in thymus suggests that the association between Mls expression and clonal deletion of self Mls-reactive T cells appears to be the general rule in inbred strains. Based on these results, implications for the nondetectable Mls-like gene products in other species besides the mouse are discussed.     

Genetics of a non-H-2 antigen that stimulates "unrestricted" helper T cells and MLR

The inheritance of antigens expressed by C3H/Tif B cells that stimulate MHC-unrestricted helper T cells from C3H/HeJ was investigated. F1 hybrids between C3H/HeJ and C3H/Tif and 39 C3H/HeJ X F1 backcross mice were characterized as to the ability of their spleen cells to stimulate a proliferative C3H/HeJ T helper cell response and to respond to helper cell activity by the development of polyclonal plaque-forming cell responses. Backcross progeny wee also typed for the following markers segregating in this cross: 1) Responsiveness to the B cell mitogen lipopolysaccharide (LPS); 2) LyM-1 allotype; 3) antigen(s) stimulating a primary non-H-2 MLR between these strains, previously ascribed to Mls locus differences, 4) expression of target antigens for cytotoxic T cells raised in the same strain combination. The antigen(s) recognized by helper cells and those stimulating primary MLR are controlled by autosomal gene(s) and segregate as a single trait. These antigens, however, are not encoded in genes linked to either the Lps or the Mls loci, and are not recognized by cytotoxic T cells raised in the same strain combination.     

Biochemical characterization of murine lymphoid alloantigen Ly-m20.2, a cell surface marker controlled by a gene linked to the Mls locus

The lymphoid alloantigen Ly-m20.2 is expressed on the majority of B cells and a wide variety of hemopoietic cells including stem cells. However, it is not detectable on T lymphocytes. Genetic studies indicate that expression of Ly-m20.2 is controlled by a gene(s) closely linked to the M1s locus. Our present biochemical analysis shows that Ly-m20.2 is a monomeric glycoprotein of 55,000 to 60,000 daltons, with no detectable intramolecular disulfide bonds. The Ly-m20.2 molecules of tissues and clonal cell lines exhibit size and charge heterogeneity that can be eliminated by the complete removal of N-linked sugars with the enzyme endo-F or by inhibiting glycosylation with tunicamycin. The resulting unglycosylated Ly-m20.2 molecule migrates as a single band of 40,000 daltons in SDS-gels and behaves as a single charge species in IEF. The Ly-m20.2 antigen was compared biochemically with two other alloantigens: LyM-1, an alloantigen whose expression is also controlled by gene(s) tightly linked to the M1s locus, and Ly-17.1, an alloantigen serologically allelic to the Ly-m20.2 antigen. Immunoprecipitates obtained with the respective LyM-1 and Ly-17.1 antisera yielded similar 55,000 to 60,000 dalton molecules from cells of the appropriate mouse strains. In the case of LyM-1, sequential immunoprecipitation provided evidence that Ly-m20.2 and LyM-1 are identical.     

Soluble Mlsa antigens: Stimulatory effect in vitro versus suppressive effect in vivo

Using a pair of congenic strains of mice differing only at the Mls haplotype (Mls locus and closely linked genes), BALB/c (Mls ^b ) and BALB.D2-Mls ^a , we have compared the in vitro proliferative responses of M1s^b lymphocytes to M1s^a antigens presented on either lymph node cells (LNC) or peritoneal adherent cells (PAC). Results showed that M1s^a-PAC are stronger stimulators than M1s^a-LNC, and furthermore, that the supernatant from M1s^a-PAC may be effective in eliciting a lymphocyte proliferative response. The proliferation in response to PAC supernatant is partially due to activation by nonspecific factor(s); however, the response in the presence of M1s^a incompatible PAC supernatant is about three times greater than the response obtained in the presence of syngeneic M1s^b-PAC supernatant, suggesting an additional stimulation by soluble M1s^a antigens. Contrasting with the ability of PAC-supernatant to stimulate a primary proliferative response in vitro, the in vivo immunization of Mls^b mice with M1s^a-PAC supernatant abrogates the specific proliferative response in subsequent one-way mixed lymphocyte cultures. This abrogation of the specific response is comparable to that observed after immunization with intact M1s^a peritoneal or spleen cells, although in the latter case the anti-H-2 proliferative response is also decreased, regardless of whether the H-2 incompatible stimulating cells express an additional incompatibility for M1s^a. The proliferation of untreated, but not of M1s^a-immunized BALB/c LNC, is stronger in cultures with DBA/2 stimulating cells (incompatible for M1s^a and other non-H-2 antigens) than in cultures with BALBM-Mls ^a cells (incompatible for M1s^a alone), and is comparable in intensity to that activated by H-2 incompatibility. We conclude that M1s^a antigens are more efficiently recognized by unprimed helper T cells when presented on PAC than when presented on LNC. In the primary proliferative response, the effects of M1s^a and other non-H-2 antigens may be cumulative. In vivo immunization against M1s^a antigens results in suppression of the specific proliferative response and, to a certain extent, of the nonspecific proliferative response (directed against both H-2 and other non-H-2 antigens). Since M1s^a antigens are obtainable in soluble form, their physicochemical purification can now be envisaged.     

Multi-gene/allele control of Mls b of CBA/H

Festenstein originally described the Mls locus as a single dominant autosomal gene with four alleles which mapped in the 13th linkage group of chromosome 1. We subsequently presented evidence indicating that the mixed leukocyte reaction (MLR) stimulatory products of DBA/2 and CBA/J were controlled by two independently segregating Mls loci and that Mls of C3H was in fact a composite of three independently segregating loci. Recently, Mls ^d of CBA/J was shown to be composed of Mls ^a of AKR and a product on C3H, which was presumed to be Mls ^c . Based on strain distributions, this product cannot be encoded by the Mls ^c originally defined by Festenstein. In the present report, three Mls specificities of CBA/H (Mls ^b ) are defined. Based on the strain distribution, we postulate that these specificities are controlled by three loci, three alleles/locus, or by some combination of the preceding two possibilities.     

Allostimulatory analysis of a newly-defined and widely-distributed Mls superantigen

We previously noted that Mls^a,c C58/J responder cells proliferated unexpectedly to H-2^k-compatible Mls^a or Mls^c prototypic stimulator cells in a primary mixed lymphocyte reaction. The present investigation was performed to evaluate whether the response of C58/J T cells to these H-2- and Mls-compatible stimulator cells could functionally identify a newly-defined member of the Mls superantigen family through its allostimulatory ability. We observed that C58/J responder cells also proliferated when cultured with H-2-compatible prototypic Mls^null, Mls^b (nonstimulatory), or Mls^a,c splenic stimulator cells. The widely distributed nature of the non-MHC ligand recognized by C58/J T cells is indicated by the finding that 11 of 12 H-2^k inbred mouse strains clearly expressed this specificity. A gradient of stimulatory capacity from low to high across this newly-defined non-MHC difference was detected with splenocytes from these different inbred mouse strains. The Mls^a,c genetic composition of C58/J was confirmed by the observation that crossing C58/J with parental B10.BR (responsive to both Mls^a and Mls^c determinants) generated F₁ progeny that were unresponsive to H-2^k-compatible Mls^a, Mls^c, or Mls^a,c stimulator cells. Like prototypic Mls^a and Mls^c, the non-MHC specificity recognized by C58/J responder cells, termed Mls^f, was particularly sensitive to radiation (versus mitomycin C) treatment of the stimulator cells, was greatly augmented after anti-IgD activation of splenic stimulator cells, was blocked with anti-MHC class II antibody, and was effectively presented by phenotypically normal female but not B cell-defective xid⁺ male CBA/N F₁ stimulator cells. Address correspondence and offprint requests to: J. J. Ryan     

T lymphocytes responding to Mls-locus antigens are Lyt-1+, 2− andI-A restricted

We have investigated primary and secondary responses of mouse splenic T cells to strong mixed lymphocyte stimulating antigens controlled by theMls locus using MHC-identical mixtures of cells. Our studies show that strong primaryMls-locus specific responses involve recognition of self I-A antigens, since BUdR and light suicide or F1 into parent radiation bone-marrow chimeras both demonstrate a preference of unprimed F1 T cells to respond to Mis-locus antigens associated with one parent's MHC antigens. Furthermore, conventional anti-I-A antisera and monoclonal anti-I-A antibody both inhibitMls-locus responses in an MHC-specific manner. Finally, as is typical of T cells responding to I-A antigens or to nominal antigens associated with self I-A,Mlslocus responses are mediated by Lyt-1⁺, 2^– cells. One striking finding in these studies was the very high frequency of cells capable of responding to Mls-locus antigens, the highest being 1/300 splenic T cells. This plus evidence for recruitment during primaryMls-locus responses may account for reports of a lack ofI-A restriction in secondary anti-Mls locus responses to strong Mls-locus antigens, a finding with which we concur. The possibility that these secondary responses between noncongenic strains of mice may be directed at other genetic loci is also discussed. These experiments leave open the question of the biological role of theMls-locus and of the very large number of T cells reactive to it.Abbreviations used in this paper MHC Major histocompatibility complex - MIg Mouse immunoglobulin - MLC Mixed lymphocyte culture - TCGF T-cell growth factor     

Genetic control of Rous sarcoma regression in chickens: Linkage with the major histocompatibility complex

Studies with two closely related inbred chicken strains show that regression of Rous sarcoma virus-induced tumors is a dominantly inherited trait, controlled by a gene within, or closely linked to, the major histocompatibility complex (B region). Strain G-B2 birds are capable of regressing Rous tumors, while strain G-B1 birds are uniformly susceptible to progressive Rous tumor development. Evidence for crossing over between the genes controlling serologically determined MHC antigens on erythrocytes and genes controlling Rous sarcoma growth was obtained. The MHC-linked gene which confers the ability to regress Rous sarcomas is designatedR-Rs-1. The allelic gene which allows for progressive tumor growth in homozygous birds is designatedr-Rs-1.     

Studies on non-H-2-linked lymphocyte-activating determinants. IV. Ontogeny of the Mls product on murine B cells.

The minor lymphocyte stimulating (Mls) locus codes for lymphocyte activating determinants (LADs) on murine B lymphocytes, but not T lymphocytes. This observation was strengthened by a series of techniques which allow deletion and addition of T and B cells. These included the use of cytotoxic antisera such as anti-Thy 1.2, anti-MTLA, anti-MBLA, and complement, and the use of a goat anti-μ antisera, and finally the use of a fluorescence activated cell sorter (FACS).The studies in this report document the organ distribution and the ontogenetic appearance of the surface LADs on the surface of B lymphocytes from DBA/2N (H-2^d, Mls^a) and CBA/J (H-2^k, Mls^d) mice. Adult-like ability to stimulate H-2 identical BALB/c (H-2^d, Mls^b) and C3H/He (H-2^k, Mls^c) responder cells appeared at about 4–5 weeks of age. Inability of neonatal cells to induce an Mls-defined MLC was found not to be due to a low frequency of B lymphocytes or to the presence of suppressor cells, but due to the absence of the Mls-coded LADs on their surface. These data support the concept that the Mls-coded LADs are present on adult B lymphocytes and are specific markers of B-cell differentiation, which is preceded by membrane IgM and the δ homologue of human IgD, Ia, and the receptor for the third component of complement.     

Topology of bovine red cell antigens as a function of the organization of their genes

Bovine erythrocytes from genetically defined animals were examined by electron microscopy for cell surface distribution of their antigens as a function of the organization of genes coding for the antigens. No blocking or inhibition of labeling was found when cells were double-labeled for two antigens whose genes resided in a) cis or trans conformations within the same blood group system (R₂ and W antigens of the C system), or b) in different blood group systems (R₂ and Z antigens of theC and Z systems, respectively). The results suggest that these antigens are probably distinct moieties on the cell surface rather than a series of determinants on a common backbone macromolecule. Genes coding for these antigens are, therefore, probably arranged in the genome as separate but closely linked genes and not as a series of multiple alleles, each allele coding for several serological determinants. A nonreciprocal increase in labeled sites was found on labeling two particular antigens within the same blood group system (R₂ and X₂ antigens of the C system). By absorption a parallel serological effect was also found for this pair of antigens.     

A new alloantigenic system associated with the Mls locus in the mouse.

An antiserum prepared by injecting C3H/HeJ mice with CBA/J tissue has been shown to react with cell surface components that are not part of any previously described system of serologically detectable alloantigens. The antiserum, which is designated AST-101, acts selectively in cytotoxic tests carried out with lymphoid cells, killing B cells, but not T cells. Phagocytic cells found in peritoneal exudates are also killed by AST-101 and complement in vitro; the sensitivity of other cell types has not been determined. Strain distribution does not indicate any association of the AST-101 system with H-2, Ly, or Thy systems; genetic analysis reveals close linkage with the mouse minor MLC-stimulating (Mls) locus. Serologic analysis also points to a close association between antigens reactive with AST-101 and the products of the Mls genes.     

The mixed lymphocyte response of senescent mice: sensitivity to alloantigen and cell replication time.

The age-dependent alteration in the proliferative response of C57B1/6J lymph node cells to stimulation by H-2- and M-locus alloantigens was examined in one-way mixed lymphocyte cultures (MLC). Balb/c (H-2^d, Mls^b) and DBA (H-2^d, Mls^a) spleen cells served as stimulating cells differing from C57B1/6J (H-2^b, Mls^b) at the H-2 and H-2 plus Mls loci, respectively. The day of peak response and the ratio of responder to stimulator cells required for optimal stimulation were the same for all the age groups (3 to 29 months) tested, irrespective of the stimulator strain used. Results obtained in MLC under optimal conditions showed a maximal response to both Balb/c and DBA/2 stimulation at the age of 6 months, followed by a gradual decline in the response with age. In order to determine whether the decline with age in mixed lymphocyte reactivity can be attributed to a reduction in the proliferative capacity of the responding lymphocytes of aged mice, cell cycle analyses were performed. Auto-radiographic studies of MLC containing lymphocytes from CS7B1/6J mice aged 6 and 24 months showed no difference in generation time, S, G₂, G₁, and M phases of the cell cycle. In addition, lymphocytes of both age groups underwent two identical mitotic waves within the period of examination. Our results determine that the functional decline with age in proliferative activity in mixed lymphocyte cultures is attributable to a neither decrease in sensitivity to alloantigen nor to a decrease in generation time or the ability to undergo several mitotic divisions, and suggest that such a decline is caused by fewer cells capable of response in old mice.     

Isolation and characterization of an I-A-restricted T cell clone with dual specificity for poly(Glu60Ala30Tyr10) (GAT) and Mlsa,dl

We have isolated a BALB/c (H-2d, Mlsb) T cell clone (JTL-G12) specific for the synthetic polypeptide antigen poly(Glu60Ala30Tyr10) (GAT) in the context of self I-A determinants and for Mlsa,d antigens in the absence of GAT. JTL-G12 proliferation in response to GAT was mapped to the Kd, I-Ad subregions by using inbred H-2 congenic and recombinant strains. In addition, monoclonal antibody directed against I-Ad but not Kd or I-As determinants blocked JTL-G12 proliferation in response to GAT presented by syngeneic splenocytes, indicating I-A restriction. The Mls cross-reactivity of this clone was verified by using a panel of inbred strains bearing the Mlsa,b,c,d alleles and by using BXD recombinant inbred strains bearing the Mlsa allele or the Mlsb allele. All of the Mlsa BXD strains of the H-2d or H-2b haplotypes stimulated JTL-G12 in the absence of GAT, whereas all of the Mlsb BXD strains were nonstimulatory. This response pattern is in complete accordance with recognition of the Mlsa determinant encoded by Mls or closely linked loci on chromosome 1. JTL-G12 proliferation in response to GAT/I-Ad and Mlsa,d determinants could be blocked with a monoclonal antibody (GK1.5) directed against L3T4, a structure involved in class II major histocompatibility complex antigen recognition. These results suggest that antigen/class II responsiveness, Mls reactivity, and expression of L3T4 can be properties of a single T cell population.     

Detection of two allotype-(Ig-1)-linked minor histocompatibility loci by the use ofH-2-restricted cytotoxic lymphocytes in congenic mice

Cytotoxic lymphocytes (CTL) were generated betweenIg-1-congenic strains BALB/c(H-2^d,Ig-1^a) andC.B-17(H-2^d,Ig-1^b) by cross-immunization in both directions and rechallenge in vitro. The effector cell populations specifically lysed target cells sharing both theH-2 haplotype and theIg-1 allele of the sensitizing strain. B- and T-cell blasts were equally good targets, suggesting thatH-2-restricted cytotoxic lymphocytes are not directed against serologically defined conventional allotypic determinants, but probably against minor histocompatibility antigens controlled by genes linked to theIg-1 complex. Competition experiments using cold target cells from a series ofIg-1^b-congenic strains of the BALB/c background (BAB-14, C.B-17, C.B-26) revealed two not yet described minor histocompatibility loci linked to theIg-1 complex: We could demonstrate that BALB/c anti-C.B-17 effector cells recognize at least two distinct antigenic determinants on C.B-17 target cells, but only one on target cells from BAB-14, which carries a recombinantIg-1 complex. From these results we conclude that one of the minor histocompatibility antigens, designated as H(C_H), is encoded by a gene linked to the heavy-chain constant-region (C_H) genes, whereas the second minor histocompatibility antigen, designated as H(V_H), is coded for by a gene linked to the heavy-chain variable-region (V_H) genes. These two new genetic markers may be useful for further analysis of the mouseIg-1 complex because the analysis of the H(C_H) and H(V_H) genes may facilitate the search for recombinants in that chromosomal region.     

Immunologic effects of whole-body ultraviolet (uv) irradiation. III Defective splenic adherent cell function in alloantigen-stimulated T-cell proliferation

The daily exposure of a mouse to ultraviolet (uv) radiation causes a selective depletion of Ia-bearing adherent cells in that animal's spleen. This depletion manifests itself in functional deficiencies in the presentation of protein antigens and haptens to T cells. The present studies demonstrate a defect in splenic adherent cells (SAC) from uv-irradiated mice resulting in defective alloantigen presentation. We show that unfractionated splenocytes and SAC from uv-irradiated mice show decreased stimulatory activity in allogeneic MLR. We then utilize this phenomenon induced by uv radiation to characterize the stimulator cell in the M locus (Mls) determinant-driven MLR. We show that the stimulator cell in Mls determinant-driven MLR is an adherent cell and demonstrate that this stimulator cell bears Ia determinants by showing that whole spleen cells and SAC from mice treated with uv radiation are inefficient stimulators of the Mls determinant-driven MLR. The importance of the Ia determinant on the stimulator cells in Mls determinant-driven MLR is corroborated by the demonstration that a monoclonal antibody directed at this determinant fully blocks the Mls determinant-driven MLR. The significance of these studies to the problem of alloreactions in vivo is discussed.     

Neonatal tolerance induction in the thymus to MHC-class II-associated antigens. II. Significance of MHC antigens in anti-Mls tolerance

Specificity of anti-Mlsa tolerance induced in BALB/c (H-2d, Mlsb) neonates was investigated by a popliteal lymph node (PLN)-swelling assay for the local graft-versus-host (GVH) reaction by injecting tolerant thymus cells into the footpads of several types of F1 hybrid mice. When thymus cells were obtained from 1-week-old normal BALB/c, they evoked enlargement of PLNs of (BALB/c X DBA/2)F1 (H-2d, Mlsb/a) [CDF1] recipients and of other hybrid recipients, heterozygous in Mlsa,c,d alleles, irrespective of the major histocompatibility complex (MHC) haplotypes. The same thymus cells did not cause the response in MHC-heterozygous F1 hybrids when the hybrids were homozygous in Mlsb, identical with BALB/c mice. Therefore, the PLN response to Mls antigens, known to be closely associated with MHC-class II antigens, was not directed to the class II antigens themselves. This enabled us to examine the effects of MHC on tolerance induction to the Mls antigens. When BALB/c neonates were injected with CDF1 bone marrow cells, complete tolerance to Mlsa-H-2d antigens of CDF1 cells was induced in the thymus, while responsiveness to Mlsa antigens in the context of H-2k and H-2b antigens, was not affected. This indicates MHC-restriction of neonatal tolerance to Mls antigens. Furthermore, when Mls and H-2-heterozygous (BALB/c X AKR)F1 (H-2d/k, Mlsb/a) bone marrow cells served as the tolerogen, thymus cells of BALB/c neonates were also tolerized to Mlsa-H-2k antigens as well as to Mlsa-H-2d antigens, which suggests the involvement of MHC, probably class II antigens of tolerance-inducing cells.     

Segregation of genetic determinants for murine glucuroinidase synthesis and loss in CXB recombinant-inbred strains

A set of recombinant-inbred strains developed from mouse strains BALB/c and C57BL/6 includes two β-glucuronidase phenotypes that are not seen in either of the progenitor strains. These new recombinant phenotypes indicate that glucuronidase levels are regulated by genes additional to the Gur locus, which is closely linked to the glucuronidase structural gene (Gus) and is known to regulate the rate of glucuronidase synthesis. In this study, induced rates of glucuronidase synthesis were determined for these recombinant-inbred strains, and rate constants for enzyme loss were calculated. The rate of synthesis was found to segregate with the Gus gene in all of the strains, and only the determinants for rate of enzyme loss recombined to give new phenotypes. It was concluded that at least two genes affect the rate of enzyme loss, that these genes are not closely linked to each other or to the Gur-Gus region on chromosome 5, and that no major determinants of glucuronidase synthesis segregate independently of Gur.     

T cell recognition of Mls. T cell clones demonstrate polymorphism between Mlsa, Mlsc, and Mlsd

The determinants encoded by the minor lymphocyte stimulating locus (Mls) are defined as determinants that induce strong T cell proliferative responses in primary mixed lymphocyte reactions. Although the Mls locus was originally described as having four alleles, a, b, c, and d, a number of recent observations have led several investigators to challenge the idea that Mls is truly a polymorphic system. To better define this system of determinants recognized at high frequency by T cells, the present studies were undertaken to evaluate the polymorphism of Mls products. In the present study, the in vitro proliferative responses of Mlsa- and Mlsc-specific T cell clones were employed to analyze Mls products. The identification of determinants recognized by Mlsa- and Mlsc-reactive clones was established by the pattern of responses to stimulators derived from congenic strains, recombinant inbred strains, and backcross mice. T cell clones and unprimed T cells gave concordant responses that confirmed the Mlsa or Mlsc specificity of the cloned populations. With the use of these two sets of Mls-specific T cell clones, the existence or absence of polymorphism of Mls-encoded gene products was examined. It was found that Mlsa-specific cloned T cells responded to Mlsa but not Mlsc stimulators, whereas Mlsc-specific clones responded to Mlsc but not Mlsa. This reciprocal pattern of specificity indicates that the Mls system as currently defined is therefore truly polymorphic. In addition, it was observed that both Mlsa- and Mlsc-specific clones were stimulated by Mlsd stimulators. In particular, the possibility that Mlsa and Mlsc are not alleles but products of different loci and that Mlsd strains are those that express both Mlsa and Mlsc is considered.