Polymorphism ofTcrb andTcrg genes in Biozzi mice: Segregation analysis of a newTcrg haplotype with antibody responsiveness

Tcrb andTcrg gene polymorphism was investigated in high (H) and low (L) responder Biozzi mice from selection I, II, and GS by Southern blot analysis with appropriateV andC probes. No polymorphism of theTcrb haplotype was detected between H and L mice in all selections which were all found to be of the BALB/c type. The H-I and H-II g genotype was of BALB/c and DBA/2 type, respectively. In contrast, a newTcrg haplotype shared by L-I and L-II mice was identified and characterized by C1, 2, 3, C4, V1, 2, 3, V5, and V6 restriction fragment length polymorphisms (RFLPs).Tcrg genotypes were not fixed in the GS selection and two additional new haplotypes were identified in two L-GS mice. An attempt was made to correlate the L-Ig genotype with the low responder status by analyzingg haplotypes among highest and lowest responder (H-1 x L-I)F₂ hybrids immunized with sheep red blood cells (SRBC). No correlation was found in this segregation study, whereas a highly significant one was established with theH-2 haplotype, a locus already known to participate in the genetic control of H-I/L-I difference. The lack of correlation between SRBC response and theTcrg genotype was consistent with the heterogenousg haplotypes found in mice of the GS selection. Together, the present results suggest that H and L mice have the sameTcrab potential repertoire and that T-cell receptor (Tcr) genes cannot be considered as immune response genes in this model. Our results also indicate that the F₂ segregation analysis, given a polymorphic gene, is suitable for an investigation of its immune response functions.     

Immune responses of mice to poly(L-Tyr-L-Glu-L-Ala-Gly) and its oligomers

C57BL/6 (H-2 ^b) mice, when immunized with the sequential polymer (T-G-A-Gly)_n and its low-molecular-weight oligomers, respond only to theα-helical oligomers with molecular weights of 9700 and above. Only the sameα-helical oligomers were able to inhibit the homologous antigen-antibody reaction. Random copolymers of GA, GT, and GAT¹⁰ did not inhibit. In vitro stimulation of peritoneal exudate lymphocyte (PETLES) cultures showed that the cellular response (T-cell) against (T-G-A-Gly)_n is antigen-specific. In vitro antigen-induced stimulation of whole spleen or lymph node lymphocytes indicated that (T-G-A-Gly)_n might also be a B-cell mitogen.     

Genetically controlled IgM hyporesponsiveness to aK. pneumoniae polysaccharide

Examination of the immune response to aKlebsiella pneumoniae polysaccharide (K47-PS) has revealed that BALB/c mice demonstrate only a very weak primary response to this antigen. The low response does not result from either a peculiar dose response curve for BALB/c mice or from differing optimal antigen concentrations for high and low responder mice. Genetic analysis indicates that this variability of response is explicable assuming two alleles at a single locus; high responsiveness is dominant. Variability of response is probably not linked to theH-2 complex since the low and high responder mice, BALB/c and B10.D2/Sn new line, respectively, share the sameH-2 haplotype (H- 2_d). Tests of F₂s, backcrosses, and appropriate congenics have not shown evidence of linkage to sex, the albinism gene, the genes controlling coat color (agouti, black, brown), or the allotype-constant-region genes. The hyporesponsiveness is apparent only in the primary (IgM) response; hyperimmunization evokes similar antibody titers in high and low responding strains.     

Genetic control of two independently segregating loci in mice to the sequential polypeptide (Tyr-Ala-Glu-Gly)n

Immune responses to the sequential helical polypeptide (Tyr-Ala-Glu-Gly)_n [(T-A-G-Gly)_n] in mice is under the control of at least two separate genes. One gene,Ir-(T-A-G-Gly)-1, which is linked, toH-2 haplotypesb, f, andr, controls the ability to respond and maps to theIA subregion. A non-H-2-linked locus,Ir-(T-A-G-Gly)-2. is responsible for the magnitude of the antibody response, which is expressed as a high, intermediate, or low level of antibody production. The antibody produced is of the IgG class, and does not crossreact even with the closely related sequential helical polymer (Tyr-Glu-Ala-Gly)_n [(T-G-A-Gly)_n]. Immune responsiveness is a dominant trait,i.e., the F₁ generations of responder x nonresponder crosses are responders. However, the data obtained with both backcross populations are not easily interpretable. The contribution of the B-cell mitogenic activity of the sequential polymer to activation of suppressor T cells is considered as a possible explanation for the backcross results. The possible role of the Ia. W29 specificity present in the mouse strains responding to both (T-A-G-Gly)_n and calf skin collagen type I in modulating responses to the polymers is discussed.     

Characterization and genetic control of the immune response to synthetic polypeptide antigens of defined geometry.

Both humoral and cell-mediated immune responses to the synthetic helical hapten-carrier conjugate poly-Glu-Tyr-Lys(TNP)-(Glu-Tyr-Ala)5 were found to be linked to the major histocompatibility locus in mice and guinea pigs. The responder mouse strains (H-2d haplotype) showed a primary IgM response with an IgG component appearing after the secondary immunization. The antibody response was accompanied by a positive DTH reaction in responder strains. Nonresponder mice (H-2b or H-2k haplotypes) showed neither IgM nor IgG antibodies and the DTH reaction was negative. Administration of the antigen as a complex with an immunogenic carrier was not effective in inducing a response in nonresponder mice. In guinea pig studies, it was found that strain 2 animals were able to mount an antibody response against the TNP-hapten and a DTH response against the polypeptide backbone. Strain 13 animals gave no anti-TNP antibodies at the lower dose levels and DTH activity was entirely negative for all doses of immunizing antigen. Replacement of the TNP hapten by the arsanilazo dipeptide derivative, BOC-gly-ARA-tyrosine, converted the nonresponder strain 13 guinea pigs into complete responders showing antibody and DTH reactions to both the hapten and the polypeptide backbone.     

Interaction ofH-2 and nonH-2 linked genes in the regulation of antibody response to a threshold dose of sheep erythrocytes

The antibody response to a threshold dose (¹⁰) of SE was studied in the High responder line (H) and the Low responder line (L) of mice obtained by bidirectional selective breeding for the character quantitative agglutinin response to an optimal dose of SE, and in interline hybrids: F₁, F₁ and both backcrosses. Whereas the interline difference in agglutinin responses at the optimal dose is due to the additive effect of about ten independently segregating loci, one of which isH-2 linked, the responsiveness to the threshold dose is determined by the effect of two loci. The direction of the dominance effect also varies with the antigen dose: high responsiveness is partially dominant at the optimal dose while at the threshold dose nonresponder character is partially dominant. The role of theH-2 linked locus was investigated. It has been demonstrated that on an identical background (equivalent to that of F₁ hybrids) this locus is responsible for 12% of the interline difference at the optimal antigen dose, and for 61% at the threshold antigen dose. For the two antigen doses, the quantitative effect of theH-2 locus is in agreement with the estimate of the number of loci obtained by variance analysis. The intervention of a second gene, non-H-2 linked, in the regulation of responsiveness to 10⁶ SE is demonstrated by appropriate assortative matings. The interaction between the two genes is discussed.     

Two distinct high immune response phenotypes are both controlled byH-2 genes mapping inK orI-A

Murine responses to immunization with 2, 4, 6-trinitrophenyl (TNP) conjugated to autogenous mouse serum albumin (MSA) in complete Freund's adjuvant (CFA) are controlled by a gene(s) in theK orI-A region of theH-2 complex. High immune responses of bothH-2 ^d andH-2 ^b mice have been mapped to this region of the major histocompatibility complex. No modifying effects were observed from genes to the right ofI-A in either responder haplotype. High responsiveness controlled byK ^b orI-A ^b is inherited with complete or partial recessivity, depending on the route of immunization and the sex of the responder. However, high responsiveness controlled byK ^d orI-A ^d is inherited dominantly. This unusual pattern of inheritance of immune responsiveness to TNP-MSA is consistent with the genetic mapping toK orI-A. TNP-MSA-specific T-cell reactivity following immunization with TNP-MSA in vivo was examined utilizing a T-cell-dependent proliferation assay in vitro with cells obtained from high or low responder mice. Genetic mapping and mode of inheritance in this assay for antigen-specific T-cell reactivity corresponded with results obtained from a plaque-forming cell (PFC) assay measuring antibody production by B cells. Both the proliferative and PFC responses are probably under the sameIr gene control. Both gene dosage effects and Ir-gene-product interaction could influence the generation of specific immune responsiveness in F₁ hybrids between high and low responders to TNP-MSA.     

T helper and T suppressor cells are restricted by the A and E molecules,respectively, in the F antigen system

The role of the A and E molecules as restriction elements was examined in the F antigen system. In the mouse the only responder haplotype known to date isk, and blocking studies with a monoclonal antibody show that in vitro T-cell proliferation is restricted by the A^k molecule. The (CBA × DBA/2) F₁ hybrid, which is a responder x nonresponder cross, is itself a nonresponder in terms of E-specific antibody production. Up to 10 days after priming, (CBA × DBA/2) F₁ T cells exhibited an E-specific proliferative response, but this diminished rapidly at later times. This diminution could be blocked with an E-specific monoclonal antibody, suggesting that suppression is restricted by the E molecule.     

Antigen-Specific T-cell factors in the immune response to poly(Tyr,Glu)-poly(Pro)-poly(Lys)

The production by T cells of an antigen-specific factor capable of replacing the T-cell function in specific antibody formation was used as a tool for studying the cellular aspects of the genetic control of immune responses. The ability of different T-cell populations to produce a cooperative signal and the ability of B-cell populations to react to this signal were studied in different mouse strains. The antigen used was the synthetic polypeptide poly(LTyr,LGlu)-poly-(LPro) —poly(lXys), (T,G)-Pro -L, the response to which was found not to beH-2-linked. It was found that the SWR strain of mice, a low responder to (T,G)-Pro -L, is not capable of producing a T-cell factor specific to this antigen, but its B cells react normally to an active factor produced in a high responder strain. In the DBA/1 strain, also a low responder to (T,G)-Pro -L, the bone marrow cells are not able to cooperate with an active T-cell factor to produce anti-(T,G)-Pro —L-specific antibodies, while their T cells do produce a (T,G)-Pro -L-specific factor. The SWR (low responder) B cells can be triggered by DBA/1 (low responder) T cells factor specific to (T,G)-Pro —L to produce an antibody response to this immunogen. These results suggest that the immune response to (T,G)-Pro -L is controlled by two genes which are expressed in different lymphocyte populations.     

Murine responses to (Tyr-Glu-Ala-Gly)n: II. H-2 and non-H-2 gene effects

Mice of the H-2^b haplotype responded to the sequential polymer poly(Tyr-Glu-Ala-Gly) in the in vitro T-cell proliferative assay, irrespective of whether they were homozygous or heterozygous at the H-2^b locus. The antibody responses of the H-2^b congenic mice to this polymer were variable, with A.BY and BALB.B showing responses better than those of C57BL/6 and C57BL/10 strains. The antibody responses of the F₁ progeny of (responder × nonresponder) strains of mice to this polymer are generally lower than the responder parents. F₁ mice with C57BL/10 background were the poorest responders. Studies with F₂ mice and backcross progenies of selective breeding of high and low antibody responder (C57BL/6 × BALB/c) F₁ to high responder C57BL/6 mice indicated that both non-H-2 genes and H-2 gene dosage effects influenced the magnitude of the humoral antibody responses. Animals having low responder non-H-2 background and only half the dosage of the responder immune response genes has greatly diminished antibody responses.     

Genetic control of the immune response in rats to the known sequential polypeptide (Tyr-Glu-Ala-Gly)n. I. Antibody responses.

In inbred rats, the antibody response to the known sequential polypeptide (Tyr-Glu-Ala-Gly)n (T-G-A-Gly)n is under the control of two independently assorting loci; (co) dominant, Ag-B-linked Ir-(T-G-A-Gly) I, controlling qualitative responsivenss, and a non-Ag-B-linked modifier locus termed Ir-(T-G-A-Gly) II, controlling the level of antibody produced. The antibody response to (T-G-A-Gly)n was solely IgG and the level of antibody produced was dependent upon Ir-(T-G-A-Gly) II for phenotypic response type.     

T(Iat)- and B(Iab)-cell alloantigens determined by theH-2 linkedI region in mice

The specificity of an antiserum directed againstI region associated (Ia) antigens is described. The serum was raised in (DBA/1×B10.D2)F₁ mice against lymphocytes of AQR mice, differing from the responder for theI region only. The serum reacts with Ia antigens expressed on B cells (Iab) as well as with Ia antigens expressed on T cells (Iat). Absorption studies indicate that B cells possess at least two Ia antigens, and one of these is shared by T cells. However, this shared antigen is not present on the surface of lymphocytes of thymectomized mice. Analysis of the strain distribution of Iab and Iat antigens revealed that the Iab antigens are present on lymphocytes of mice carrying theIA ^k subregion and that the Iat antigens are present on lymphocytes of mice carryingI region genes of theH-2 ^k haplotype located between theIA andIB subregions. This conclusion is based on the analysis of the antiserum's reactivity with T and B cells of the strains B10.A(2R), B10.A(4R) and B10.HTT: the serum reacts with B and T cells of B10.A(2R) but only with B cells of B10.A(4R) mice and only weakly with T cells of B10.HTT mice.Abbreviations ALG antimouse lymphocyte globulin from rabbits - B cells bone marrow derived lymphocytes - B10 C57BL/10Sn mice - D1D2F₁ (DBA/1×B10.D2)F₁ hybrid mice - GVHR graft-vs-host reaction - Ia I region associated antigen - Iab on B cells - Iat on T cells - MLR mixed lymphocyte reaction - T cells thymus-derived lymphocytes - Thy-1 thymus antigen 1, formerly called theta - Tx-Lyc lymphocytes of thymectomized, ALG treated, lethally irradiated and anti-Thy-1 treated bone marrow reconstituted mice - 2R B10.A(2R)/SgSn mice - 4R B10.A(4R) mice     

Multigenic regulation of the primary immune response to ovalbumin in mice

At least four genes regulate the primary immune response to ovalbumin in mice. The ability to be sensitized to transfer delayed type hypersensitivity to ovalbumin is controlled by two genes. One gene,OVA-, is linked to theH-2 complex and maps to the left ofI-E. The linkage of the other gene,OVA-Bg1, has not been determined, but it segregates independently of theLy M locus, of the heavy chain allotype genes and of certain genes controlling coat color. At least two genes regulate the ability to respond with a primary antiovalbumin antibody response. One gene,OVA-, is linked to theH-2 complex and maps to the right ofI-E. Discordance of the minimum dose of antigen needed to elicit delayed type hypersensitivity response and antibody suggests that non-H-2 gene(s) regulating the primary antibody response are different fromOVA-Bg1.Abbreviations used in this paper BSA bovine serum albumin - DTH delayed type hypersensitivity - H-2 major histocompatibility complex of mouse - Ir gene — immune response gene - OVA ovalbumin - SRBC sheep red blood cells     

Genetic and immunological characterization of naturally occurring recombinant B3 rats

The B-stock population of rats was bred for homozygosity at the loci controlling coat color. In this process, theAg-B1 andAg-B3 haplotypes became fixed in Hardy-Weinberg equilibrium. Extensive immunization and absorption studies showed that the specificities in the B-stock rats homozygous for theAg-B1 haplotype were the same as those found in the inbred F344 strain (Ag-B1), and that the specificities in the rats homozygous for theAg-B3 haplotype were the same as those found in the inbred BN (Ag-B3) strain. A homozygous line derived from the rats carrying theAg-B3 haplotype (B3) has the mixed lymphocyte reactivity and antibody responsiveness to poly (Glu⁵²Lys³³Tyr¹⁵) characteristic of the inbred strains in theAg-B4 group. Thus, it represents a naturally occurring recombination between the loci controlling MLR and immune responsiveness, on the one hand, and those controlling the Ag-B antigens on the other. Antibody responsiveness segregated with theAg-B3 haplotype in crosses between the B3 homozygotes and the low responder BUF and M520 strains; hence, this recombination is a stable one. There was no linkage of antibody formation or haplotype to coat color. The finding of a strain with a naturally occurring recombination in the major histocompatibility complex between the loci controlling mixed lymphocyte reactivity and the Ag-B histocompatibility antigens provides evidence for the separateness of these loci. Since the portion of the genetically determined mechanism controlling antibody responsiveness which is linked to the MHC was that characteristic of the MLR type, it too must lie outside the region defined by the serological specificities of theAg-B haplotype.     

Polygenic control of quantitative antibody responsiveness: restrictions of the multispecific effect related to the selection antigen

Among the differences observed between the various high (H) and low (L) antibody responder lines of mice resulting from distinct bidirectional selective breedings, one of the most puzzling is the variation in the multispecific effect, i. e., in the modification of antibody responses to antigens unrelated to those used during the selection. The best examples are the H and L lines of selection IV, selected on the basis of responses to somatic antigen of Salmonella which do not differ in their antibody responses to sheep erythrocytes (SE). However, a wide range of variability is observed in the responses of (H_IV x L_IV)F₂ hybrids to this antigen, and it was therefore hypothesized that distinct groups of genes might regulate antibody responses to SE and the somatic antigen. Indeed, a new selection (IV-A) for anti-SE responsiveness started from these (H_IV x L_IV)F₂ successfully produced a high and a low anti-SE responder line. The results of selection IV-A and the variance analysis of (H_IV-A × L_IV-A)F₂ hybrids are reported. They are roughly similar to those in selection I, also carried out for anti-SE responsiveness. In vivo attempts to identify the major regulatory mechanism which contributes to the interline difference indicate that the efficiency of macrophage accessory function has been modified in selection IV-A, as was observed in selection I, whereas this function did not differ in Hév and Lév lines. Probably in relation to the involvement of macrophage function there is a notable increase of the multispecific effect in selection IV-A when compared with selection IV. The results of selection IV-A demonstrate that responsiveness to heterologous erythrocytes and to somatic antigen of Salmonella are under separate polygenic control operating through distinct regulatory mechanisms. The choice of the selection antigen and immunization procedure is of major importance for defining the gene interaction operating in each selective breeding experiment and the extent of its multispecific effect.Abbreviations used in this paper f. ag. S. flagellar antigen of Salmonella - H high responder line (roman numeral is the selection number) - h₂ heritability - HE human erythrocytes - HoGG horse gamma globulin - L low responder line (roman numeral is the selection number) - PE pigeon erythrocytes - R response to selection - RGG rabbit gamma globulin - S selection differential - s. ag. S. somatic antigen of Salmonella - SE sheep erythrocytes     

Functional similarities of AeEα Ia molecules as determined by analysis with T-cell clones

Recognition of A_eE Ia antigens at the functional level was investigated using T-cell clones. The reactivities of an alloreactive and an antigen-reactive clone, both of which recognized A_eE Ia molecules, were compared on a panel of stimulator/antigen-presenting cells of various genotypes. The two clones recognized all tested A _e ^b E ^x Ia molecules, where x is a haplotype capable of expressing an Ia.7-bearing E polypeptide. Ia antigen recognition by either clone could be inhibited by the monoclonal antibody Y-17, which recognizes a combinatorial serologic determinant on certain A_eE molecules. There were no differences in the recognition of Ia by the alloreactive versus the antigen-reactive clone, suggesting that Ia antigens are recognized by the two clones in a fundamentally similar way. The recognition of these various Ia molecules by the two cloned T-cell lines provides evidence that the E polypeptides from H-2 haplotypes k, d, r, and u are functionally indistinguishable.Abreviations MHC major histocompatibility complex - Mb myoglobin - MLR mixed leukocyte reaction - PBS phosphate buffered saline - APC antigen presenting cell - KLH keyhole limpet hemocyanin - GAT poly (glut⁶⁰ alai³⁰ tyr¹⁰)n - (TG)-A—L poly (L-tyr, L-glu)-poly (D, L-ala)—poly L-lys - GLPhe poly (glu⁵⁵ lys³⁶ phe⁹)n     

Alloreactivity of an OVA-specific T-cell clone

A T-cell clone (Lyl-03) derived from BALB/cBy mice, though highly specific for OVA/A^d, reacted to allogeneic spleen cells of 6 of 12 H-2 haplotypes tested. The reactivity to each particular H-2 haplotype required the expression of a non-major histocompatibility complex (MHC) gene product present on the B cells of certain strains of mice. All the alloreactive responses were MHC restricted and were inhibited by class II-specific and L3T4-specific monoclonal antibodies. The non-MHC gene product, X, is a new lymphocyte-stimulating determinant that is not expressed in mice with the xid defect. We favor a model that proposes two independent sites (or receptors) for X and the class II molecule. Contrary to previous models for alloreactivity, the anti-MHC site is not directed to a polymorphic receptor for self-class II epitope on the foreign class II molecule, but rather to a conserved determinant present on both self- and allo-class II molecules. If there is only one antigen receptor on the T-cell clone Lyl-03, then anti-X receptor must bind to a cross-reactive determinant found on immunogenic OVA and the non-MHC coded gene product expressed on the cell surface membrane. We further postulate that class II plus X recognition may be a general rule for alloreactive as well as autoreactive responses. Thus, both allo-class II and allo-class I reactive T cells are similar in that both bind a non-MHC coded gene product prior to activation.Abbreviations used in this paper: APC antigen-presenting cell(s) - Con A concanavalin A - Cl. clone - DME Dulbecco's modified Eagle's medium - FCS fetal calf serum - H-2 histocompatibility-2 - MHC major histocompatibility complex - MLR mixed lymphocyte response - Mls mixed lymphocyte stimulating - OVA chicken ovalbumin - X unknown cell-surface antigen - xid immunodeficiency mapped to the X chromosome     

Functional requirements of (Phe,G)-A--L-specific T-cell clones of (H-2 b x H-2 kF1 origin

T-cell clones specific for the synthetic polypeptide antigen poly(LPhe, LGlu)-poly(DLAla)--poly(LLys) of (C57BL/6 x C3H/HeJ)F₁ origin were tested for their biological activities. One group of clones was restricted in its proliferative response to the H-2 ^b haplotype, the second to the H-2 ^k haplotype, and the third to the F₁ unique Ia determinants. All the clones which proliferated in response to antigen secreted interleukin-2 (IL-2) following stimulation. The H-2 restriction of the IL-2 secretion was the same as that of the proliferation. Two of the clones tested, C.6 and C.10, could provide help to B cells in antibody production. However, the genetic restriction profile of the helper activity was less stringent than that for the proliferative response. Thus, C.6, which proliferated in the presence of F₁ antigen-presenting cells only, could help B cells and accessory cells of C3H/HeJ. C.10, which was restricted in its proliferative response to the H-2 ^b haplotype, could collaborate with B cells and accessory cells of the H-2 ^k haplotype as well. The antibody response of both clones was restricted to the parental or F₁ strains.Abbreviations used in this paper (T, G)-A-L poly-(LTyr, LGlu)poly(DLAla)--poly(LLys) - (Phe, G)-A--L poly(LPhe, LGlu)-poly(DLAla)--poly(LLys) - APC antigen-presenting cells - Con A concanavalin A - FCS fetal calf serum - IL-2 interleukin-2     

Evidence for distinct polygenic regulation of antibody responses to some unrelated antigens in lines of mice selected for high or low antibody responses to somatic antigen of Salmonella

The effect of the selective breeding of mice for high or low antibody production to complex immunogens is largely nonspecific, since it modifies the responsiveness of high (H) and low (L) lines to many antigens unrelated to the selection antigen. However, the nonspecific effect of the polygenic control operating in these lines is not a general feature. For example, the group of genes in selection IV, carried out for responsiveness to somatic antigen of Salmonella, does not modify the responses to sheep erythrocytes (SE). Despite equivalent responses in H and L mice of selection IV, a large variability was found in individual responses of F₂ interline hybrids, which demonstrates the presence of alleles with high or low effect on responses to SE. A selective breeding (Selection IV-A) was therefore initiated from this F₂ population for responsiveness to SE. A progressive interline divergence occurred during the first seven generations of selection; the interline separation was due to polygenic regulation (about four independent loci from a preliminary estimate).Equivalent responses to the s antigen of Salmonella are observed in the two lines. This constitutes additional evidence for distinct polygenic regulation of responses to SE and to somatic antigen. Moreover, the pattern of responses to several unrelated antigens (nonspecific effect) also differs between Selections IV and IV-A.Abbreviations H high responder lines - L low responder lines - s somatic antigen of Salmonella - f flagellar antigen of Salmonella - R response to selection - S selection differential - F₀ foundation population - h² heritability (realized) - RGG rabbit gamma globulin - CE chicken erythrocyte - HE human erythrocyte - PE pigeon erythrocyte - SE sheep erythrocyte     

Delayed-type hypersensitivity responses to H-Y: Characterization and mapping ofIr genes

This paper examines the delayed-type hypersensitivity (DTH) response to male (H-Y) antigen(s). Female mice of theH?2 ^b haplotype developed delayed footpad reaction to syngeneic or allogenic male thymus and spleen cells after priming with syngeneic male thymus and spleen cells. The reaction peaks at 24 h, has classical DTH histology and is specific to H-Y antigen as it is not elicited with female cells. Cell transfer studies show that donor/recipient matching at theI?B ^b subregion is necessary for sucessful transfer of DTH and that the effective primed population is Thy-1⁺, Lyt-1⁺, 2^?. DTH response to H-Y antigen appears to be confined to mice of theH?2 ^b haplotype. There appears to be a lack of associative recognition between H-Y antigen and MHC-coded determinants in the effector phase of DTH, and macrophage processing of H-Y seems likely, since nonresponder haplotypes can elicit the DTH response. Studies withH?2 ^b recombinant mouse strains indicate that the dominantIr gene is located in theI?B region. Female F₁ hybrid mice derived from matings of strains not involvingH?2 ^b haplotype failed to develop DTH to H-Y. In summary, these data imply that a complete correlation exists between DTH to H-Y and the ability to reject male skin graft, suggesting that the effector mechanisms of skin-graft rejection may closely involve DTH cells.