Qed-1--a target for unrestricted killing by T cells

Response to Listeria monocytogenes in Mice Lacking MHC Class Ia Molecules

MHC class Ia-deficient mice (H2 Kb−/− Db−/−) inoculated with the intracellular pathogen Listeria monocytogenes (LM) displayed a three- to fourfold expansion of splenic CD8+ T cells 6 days following infection. Culture of these spleen cells in vitro gave rise to CTL that recognized LM-infected target cells and were restricted by the class Ib molecules, Qa1b and M3. Exposure of target cells to heat-killed LM (HKLM) rather than live bacteria did not result in CTL-mediated lysis. Target cells pulsed with three LM peptides known to bind M3, f-MIGWII, f-MIVTLF, and f-MIVIL, were recognized by effector cells from both B6 and Kb−/− Db−/− animals. In vivo analysis showed that B6 and Kb−/− Db−/− mice clear LM from the spleen and liver rapidly with similar kinetics, whereas TAP.1−/− mice, which are deficient in class Ia and Ib molecules, clear LM slowly upon infection. To establish the in vivo role of CD8+ T cells in Kb−/− Db−/− animals, we showed that depletion of such cells from the spleens of immune mice prevented the adoptive transfer of protective immunity to syngeneic recipients. Spleen cells from Kb−/− Db−/− mice were also capable of generating responses directed against syngeneic as well as allogeneic class Ia molecules in vitro. Thus, class Ia-deficient animals have a CD8+ T cell repertoire capable of recognizing both class Ia and class Ib molecules and can generate protective immunity to LM.

H2-M3 Presents a Nonformylated Viral Epitope to CTLs Generated In Vitro

Most CTL responses to epitopes from influenza virus are restricted by MHC class Ia molecules. However, a synthetic peptide corresponding to residues 173 to 190 of influenza A/JAP/305/57 hemagglutinin (HA) can induce, in vitro, a CTL response to peptide presented by a mouse class Ib molecule encoded by a gene telomeric to H2-Q. Here, we identify the molecule as H2-M3 and show that the last five residues of HA173–190, MLIIW, is the minimal epitope for CTL recognition. Cells that express M3wt, from C57BL/6 or BALB/c mice, are sensitized by both MLIIW and the longer peptide HA173–190, whereas cells that express M3f, from A.CA or B10.M mice, are sensitized only by MLIIW; a single amino acid change at residue 31 (V→M) of M3 accounts for this difference. Although M3-restricted CTLs preferably recognize N-formylated epitopes, i.e., those of mitochondrial or prokaryotic origin, our findings show that M3-restricted primary CTL responses can be generated in vitro against nonformylated epitopes.

Kinetic analysis of Qa-1-specific cloned cytotoxic T lymphocytes: lytic parameters and evaluation of cellular inhibition

A kinetic analysis of lysis assay was used to compare cytolysis of target cells expressing different allelic Qa-1 determinants by a Qa-1b-specific cytotoxic T-lymphocyte clone (CTL). Although this clone specifically recognized the Qa-1b determinant it also recognized the Qa-1c and Qa-1d determinants to a lesser extent. The maximum rate of lysis against Qa-1b targets was 10-fold faster than against Qa-1c or -1d targets. The affinity of the CTL clone for the Qa-1b and -1c target cells was the same, but significantly less for Qa-1d targets. The pattern of inhibition observed for target and inhibitor cells in these experiments was competitive. These studies demonstrated a greater similarity between the Qa-1b and -1c determinants, compared with Qa-1d. Kinetic analysis of lytic reactions allowed for quantitative evaluation of the similarities and differences between various target cell populations to an extent not possible using conventional cell-mediated assays.

Immunodominance in the T-cell response to multiple non-H-2 histocompatibility antigens. II. Observation of a hierarchy among dominant antigens

Immunization of C57BL/6 mice with BALB.B spleen cells in vivo and subsequent boosting in mixed lymphocyte culture result in the generation of cytolytic T lymphocytes (CTLs) which are specific for a limited number of immunodominant antigens. Experiments are described which suggest the existence of a hierarchy of immunodominance in this donor: host combination. Two antigens, CTT-1.3 and CTT-2.3, are dominant in the C57BL/6 anti-BALB.B CTL response. The distribution of these antigens among CXB recombinant inbred (RI) strains suggests that they segregate as single gene traits. Elimination of the CTT-1.3 and CTT-2.3 antigens by complementation in the responder, or elimination from the priming and boosting stages by the selection of CXB RI strain mice as responders or stimulators, reveals a second level of immunodominant antigens which include CTT-3.3 and CTT-4.3. CXB mice which express one of the CTT-1.3 or CTT-2.3 antigens will produce CTLs specific for the other antigen upon priming and boosting with BALB.B cells. Expression of both antigens in responders results in the generation of CTLs specific for the second level, dominant antigens. Immunodominance is not confined to the C57BL/6 anti-BALB.B system but can also be observed in the BALB.B anti-C57BL/6 and B10.D2 anti-DBA/2 systems. Finally, generation of CTLs following priming and boosting with dominant and dominated antigens presented on different cells confirmed that immunodominance can only be observed when the dominant and dominated antigens are presented on the same cells. These observations suggest that immunodominance is revealed at the level of antigen-presenting cells primarily involved in vivo priming.

Mta, the maternally transmitted antigen, is determined jointly by the chromosomal Hmt and the extrachromosomal Mtf genes

Mus spretus from four stocks, originating in Spain, Portugal, and Morocco, were tested for the maternally transmitted antigen, Mta. All expressed a variant form not found in other species of mice. Analysis of appropriate crosses with inbred mice showed that the spretus form of Mta is determined by a new allele, c, of the Hmt gene. The Hmtc allele has been isolated in coupling with four different H-2 haplotypes. It is possible to raise CTL specific for the spretus form of Mta. The maternally transmitted factor, Mtf alpha s, of spretus mice determines, in conjunction with the Hmta allele of C57BL/6, an Mta that is indistinguishable from the common form found in C57BL/6 and most other inbred mice. Our experiments show that the specificity of the cell surface antigen Mta is governed jointly by the cytoplasmic gene Mtf and the chromosomal gene Hmt. We propose that Hmt encodes a class I histocompatibility antigen that acts as a restricting element for the Mtf gene product, thus meeting the requirements of T killer cell recognition.

Genetics of the rat CT system: its apparent complexity is a consequence of cross-reactivity between the distinct MHC class I antigens RT1.C and RT1.A

The rat CT antigens are a system of medial histocompatibility antigens linked to RT1, the rat major histocompatibility complex (MHC). They have aroused interest firstly because, despite their extreme serological weakness, they are targets for 'unrestricted' cytotoxic T lymphocytes (CTL); and secondly because they have appeared to represent a complex genetic system in terms both of the number of genetic loci involved and the number of distinguishable antigenic specificities expressed. The CT system was originally defined by the reactions of LEW anti-F344 (RT1l anti-RT1lv1) secondary in vitro CTL. These CTL reacted strongly on DA(RT1av1) targets, but much more weakly on AUG or PVG (RT1c) targets. We have used the recently derived RT1 recombinant rat strains PVG.R19 (RT1.Aav1Iav1Cc) and PVG.R20 (RT1.AcIcCav1) to investigate the genetic control of this system. Contrary to previous interpretations, the results are consistent with a model in which CT is a single locus, which maps to the RT1.C region. In addition, our results demonstrate that there is cross-reactivity of anti-RT1C CTLs on RT1A products, and we suggest that the earlier placement of a CT locus in the RT1.A region was probably incorrect and a consequence of this cross-reactivity.

Differential resistance to growth of a tumor expressing incompatible minor alloantigens reflects regulatory influences rather than differences in anti-minor-CTL-P frequencies

In previous studies it was found that BALB/c (H-2d) was more susceptible than (BALB/c X A)F1 (H-2d X H-2a) to a tumor bearing multiple mismatched minor histocompatibility antigens, the DBA/2 (H-2d) mastocytoma P815, and that this resistance was H-2 linked. In the present studies the immunologic basis of this effect was examined by comparing the cytotoxic-T-lymphocyte (CTL) responses of BALB/c with those of (BALB/c X A)F1. Despite the BALB/c X A)F1's 34-fold greater resistance to P815 in vivo, the numbers of effector cell precursors were found to be similar in the two hosts as shown by (a) similar anti-P815 CTL responses in vitro with T-cell growth factor, (b) similar secondary anti-DBA/2 MiHA responses after in vivo priming with irradiated P815, and (c) similar frequencies of anti-DBA/2 CTL precursors by limiting-dilution analysis. However, priming with proliferating P815 in vivo revealed a defect in the BALB/c animals: Spleen cells from such animals were unable to control the growth of contaminating P815 cells in vitro or to mount strong secondary CTL responses to DBA/2 antigens. The defective priming of BALB/c could be corrected when DBA/2 spleen cells were added to the P815 inoculum. This impaired priming by living tumor cells was not seen in (BALB/c X A)F1. It is concluded that the use of living P815 tumor cells revealed a defect in immunoregulation in BALB/c mice, which rendered them susceptible to tumor growth in spite of apparently adequate numbers of anti-minor-CTL precursors. How the additional H-2 products expressed in the (BALB/c X A)F1 might correct this defect is discussed.

Correlation of Qa-1 determinants defined by antisera and by cytotoxic T lymphocytes

Cytotoxic T lymphocytes (CTL) activated in H-2 identical, Qa-1 disparate mixed leukocyte cultures recognize H-2-nonrestricted target antigens indistinguishable by strain or tissue distribution from serologically defined Qa-1 antigens. Cloned Qa-1-specific CTL define determinants encoded by four Qa-1 genotypes; we used anti-Qa-1 sera in antibody blocking experiments to determine if these determinants reside on molecules recognized by Qa-1-specific antibodies. Antisera containing Qa-1.1-specific and TL-specific antibodies blocked recognition of two CTL-defined determinants associated with Qa-1a. Although both Qa-1 and TL molecules are expressed on activated T cells from appropriate strains, our studies indicated that the CTL recognized Qa-1, not TL. In addition, anti-Qa-1.2 serum inhibited CTL recognition of Qa-1b- and Qa-1c-encoded determinants. Qa-1d target cells are unique in that they express determinants recognized by anti-Qa-1a CTL and by anti-Qa-1b CTL. Killing of Qa-1d targets by anti-Qa-1a CTL was not inhibited by anti-Qa-1.1 serum, but was partially inhibited by anti-Qa-1.2 serum. Cytotoxicity of Qa-1d cells by one anti-Qa-1b CTL clone was inhibited by both anti-Qa-1.2 and anti-Qa-1.1 sera, indicating close association of both serological determinants with the determinants recognized by the CTL. Thus, all of the CTL-defined Qa-1 determinants resided on molecules recognized by Qa-1-specific antibodies, but anti-Qa-1a CTL and Qa-1.1-specific antibodies did not have identical specificities.

Polymorphism of Qa and Tla loci of the mouse

Congenic lines carrying H-2 haplotypes derived from wild mice were typed serologically with polyclonal and monoclonal antibodies specific for Tla, Qa-1, and Qa-2 antigens. The typing revealed the presence of a minimum of five Tla, four Qa-1, and three Qa-2 alleles in the 32 lines. Two new Tla, two new Qa-1, and one new Qa-2 alleles could be described. This polymorphism of Tla and Qa loci is lower than that detected at the K and D loci in the same lines. The serological typing for Qa-2 antigens correlates remarkably well with previously published results of typing with cytolytic T lymphocytes. This correlation supports the identify of loci detected by the two methods.

T-cell hyperreactivity of NZB mice against H-2 identical cells. Equal cytotoxic T lymphocyte precursor frequency against H-2 allogeneic and H-2 syngeneic target cells in NZB

NZB mice serve as a model for human systemic lupus erythematodes. T-cell abnormalities in this strain have previously been described. In this paper the cytotoxic T lymphocyte precursor (CTL-p) frequencies of NZB mice against H-2 allogeneic and H-2 syngeneic cells are investigated and compared with those of the normal strain BALB/c. The CTL-p frequency in NZB lymphocytes against H-2 allogeneic cells equals that in normal mouse strains (i.e. 1/7500). The NZB anti BALB/c response is in the same order of magnitude. No corresponding BALB/c anti NZB response was elicited. The results suggest abnormally high sensitivity of NZB CTL-p to helper signals.

MHC epitopes of KS and Dd restrict the same population of cytolytic T lymphocytes

When A. SW (H-2S) mice are immunized with B10.S (H-2S) epidermal cells, cytolytic T lymphocytes are evoked that efficiently lyse B10.D2 (H-2d) as well as B10.S target cells. Immunogenetic analysis of this apparent H-2-unrestricted killing revealed that the most plausible explanation was a sharing of an H-2-restricting epitope by H-2KS and H-2Dd molecules.

Evidence for a new lymphocyte-stimulating determinant (Lsd) detected by alloreactive T cell lines

Three alloreactive T cell clones are described which reveal a new lymphocyte-stimulating determinant (Lsd) controlled by a gene on chromosome 1 of the mouse but different from and possibly centromeric to Mls. Two clones were originally isolated as anti-H-2b-specific and showed and retained cross-reactivity to Lsd (clone OD3, BALB/c anti-C57BL/6; clone KB37, B10.BR anti-C57BL/10). The third clone (BD7, C57BL/6 anti-CBA/J) was probably originally directed against Lsd. So far, Lsd is only characterized by stimulation of T cell proliferation, and its physiological function is not yet known.

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

In this second part of the Second Listing, we describe genes that constitute the H-2 complex proper. Here, we define the complex functionally as consisting of class I and class II loci (see Klein et al. 1983a). The H-2-associated complement loci and the Neu-1 locus have been described in the first part of the Second Listing (Klein et al. 1982), but for completeness we list them here again in some of the tables. We include into the H-2 complex the cluster of Qa and Tla loci, which we consider as class I loci (Klein et al. 1983). The genetic map of the definitely established loci appears in Figure 1 and is based on the recent results of molecular genetics studies (Steinmetz et al. 1982 a, b). For historical reasons we also describe loci (regions, subregions) that were once thought to be part of the H-2 complex but either they have since been withdrawn, or their actual existence is at present uncertain. We first list loci (regions, subregions) that have been designated by capital letters (we call it Madman's Alphabet because of the frivolity with which symbols have been introduced and then withdrawn again), and then other loci believed to be associated with the H-2 complex. As in the First Listing (Klein et al. 1978), the core of the review in the Second Listing constitutes the tables of H-2 haplotypes, antigens, and determinants.

Primary cell-mediated lympholysis response to a maternally transmitted antigen

Mta-specific cytotoxic T lymphocyte (CTL) can be generated in primary cultures of (NZB X B10.D2)F1 spleen cells with H-2-compatible BALB/c stimulator cells. The CTL lyse reciprocal Mta+ (B10.D2 X NZB)F1 as well as H-2-disparate targets, such as B10, B6, and B6-Tlaa; they do not lyse targets from NZB or any F1 hybrid of an NZB mother. The lysis of 51Cr-labeled B10 targets is completely inhibited by unlabeled targets from Mta+ (B10.D2 X NZB)F1, but not from the reciprocal Mta- F1, thus demonstrating H-2-unrestricted lysis of Mta.

Suppressor T cells activated in a primary in vitro response to non-major histocompatibility alloantigens

Normal mouse spleen cells are not capable of mounting a primary cytotoxic T lymphocyte (Tc) response to non-H-2 alloantigens in vitro, although a good secondary H-2-restricted response is observable after in vivo immunization of the responder animals. Suppressor cells are generated in such a primary responses provided a Mls incompatibility exists between the responder and stimulator. These suppressors are not antigen specific, are Thy-1+, Lyt-1+, 2-, I-J-, and are highly radiosensitive. The suppressor cell precursors in normal spleen express the same phenotype. These suppressor cells are probably implicated in the lack of a primary Tc response in a primary mixed lymphocyte reaction across non-H-2 incompatibilities that include an Mls difference.

Mta, a maternally inherited cell surface antigen of the mouse, is transmitted in the egg

Mta is a maternally transmitted cell surface antigen found in most mouse strains. It serves as a target for unrestricted T killer cells. All 49 embryos transferred between positive and negative mothers, even as early as 10-15 hr after fertilization, developed into mice with the Mta type of their original mothers. Therefore the genetic element that determines expression of Mta must be transmitted by the egg. Mta+ and Mta- lymphocytes, coexisting for months in lethally irradiated F1 mice reconstituted with a mixture of parental bone marrow cells, retained their Mta type. Thus Mta does not spread by infection.

Primary in vitro cytotoxic T cell response to non-major histocompatibility complex alloantigens in normal mice

We have shown for the first time that it is possible to consistently generate a primary in vitro cytotoxic T cell (Tc) response to non-major histocompatibility complex alloantigens using responder cells from a normal mouse strain. This was achieved by carrying out, in the generating phase, a limiting dilution procedure in which it appears that suppressor cells that inhibit Tc activation or expansion are too dilute to manifest their effect. Moreover, the response was observed in mouse serum-(MS) as well as fetal calf serum- (FCS) supplemented media, an important finding in the light of the anomalous nonspecific effects induced by FCS. The cytotoxic response produced in MS-supplemented media was shown to be highly specific in both the generating and effector phases, whereas the responses in FCS had a strong nonspecific component.

Helper T cells for cytotoxic T lymphocytes need not be I region restricted

We investigated the antigenic requirements for restimulation of H-2- restricted cytolytic T lymphocytes (CTL) in vitro to determine whether H-2 I region-restricted helper T cells are required in these responses. In one set of experiments, we studied the in vitro response of (responder x nonresponder)F(1) female T cells to the male antigen H-Y. We chose to examine this response because it has been suggested that the defect in nonresponder strains is a failure of helper T cells to recognize H-Y in association with nonresponder I region determinants. However, we find that nonresponder male stimulator cells are as effective as F(1) male stimulator cells at inducing H-Y-specific CTL responses. This finding calls into question reports that secondary CTL responses to H-Y are dependent upon the activation of H-Y- specific helper T cells restricted to responder type I region determinants. In a second set of experiments, we examined the requirements for restimulation of H-2-restricted T cells specific for minor-histocompatibility antigens from long-term mixed lymphocyte cultures. These cultures were established by repeatedly restimulating cultures of specific T cells with H- 2-matched stimulator cells expressing foreign minor histocompatibility antigens. We found that H-2D-restricted T ceils, including CTL, could be restimulated with cells that were matched with the responding cells at only the D region genes. This response did not appear to result from positive allogeneic effects or from antigen processing and "representation" by responder type APC that might contaminate the cultures. Thus, we find no evidence for a requirement for I region-restricted helper T cells in these CTL responses. However, helper T cells are required because we find that CTL lines derived by limit-dilution cloning from these long-term MLC are absolutely dependent upon exogenous helper factors for growth. The most simple interpretation of these results is that the helper cells are restricted to H-2 antigens other than I region antigens or to antigens that code outside of the H-2 complex. Finally, we show that factor-dependent CTL lines must recognize their specific antigen to proliferate, even in the presence of exogenous factors. The requirement of activated CTL for antigen to proliferate provides an explanation for how specific CTL can be selectively enriched in MLC by specific antigen stimulation. Furthermore, it is at variance with reports that memory CTL or activated CTL require only interleukin 2 for restimulation.

Rat major histocompatibility RT1.C antigens of restricted tissue distribution consist of two polypeptide chains with molecular weights of about 42 000 and 12 500

The RT1.C region has recently been defined genetically as a third region of the rat major histocompatibility system, RT1, and has been shown to code for cell-surface antigens with restricted tissue distribution (present on lymphocytes and absent from red blood cells and liver) and for target antigens of unrestricted cytotoxic T lymphocytes. Immunoprecipitation with C-antigen-specific alloantisera and SDS-PAGE analysis, reveal that C-region products are glycoproteins composed of molecules of 40 500-43 000 and 12 500 molecular weight, respectively. Thus, the RT1.B region, which codes for class II molecules, is flanked by RT1 regions which determine class I molecules (as defined biochemically), which are either expressed ubiquitously (RT1.A antigens) or in a restricted manner (RT1.C products). The homology to H-2Qa antigens is discussed.

Polymorphism of a Qa-1-associated antigen defined by cytotoxic T cells. I. Qed-1a and Qed-1d

Tlad mice have a distinct Qed-1 allele, Qed-ld. Its product is detected by cytotoxic T cells raised in C57BL/6 (H-2b, Tlab) mice against cells from a new recombinant, B6-TL.123+ (H-2b, Tlad/b). Qed-1d is also found on cells from B10.M, A.CA and B10.STC90 mice. It cross-reacts weakly with Qed-1b (C57BL/6 x BALB/c)F1 anti-B10.A(5R) effectors discriminate Qed-1a and Qed-1d, while C3H/HeJ anti-B10.BR effectors cross-react extensively. CB6F1 anti-5R effector cells also discriminate between the Qed-1 antigens of B6-Tlaa (H-2b, Tlaa) and those of B10.BR and other H-2k, Tlaa strains.

Role of non-H-2 antigens in the cytotoxic T cell response to allogeneic H-2

A limiting dilution assay was used to compare the frequency of cytotoxic T lymphocyte precursors (CTL-P) which respond to H-2 antigens presented with additional background differences, with the frequency of CTL-P which respond to H-2 antigens on a self background. Individual cultures were divided and assayed for cytotoxic activity on the two targets sharing H-2, but not the background; no cultures were seen which clearly killed one and not the other, and the same frequency of CTL-P was measured on target cells that differed from the responder only at H-2 and on target cells that differed also in the background, irrespective of the background of the stimulator. Thus, the assumption that allospecific cytotoxic T lymphocytes (CTL) recognize H-2 plus minor histocompatibility antigens dose not serve as an adequate explanation for the high frequency of allospecific CTL. The data also suggest that the two allelic forms of beta2-microglobulin do not contribute to the alloantigenic determinant.

Immunodominance in the immune response to "multiple" histocompatibility antigens

Cytotoxic effector T cells putatively specific for multiple non-H-2 histocompatibility (H) antigens were generated by immunizing and boosting C57BL/6 and B6.C-H-2d mice with BALB.B and BALB/c stimulator cells, respectively. The generated effectors were tested for cell-mediated lympholysis on a panel of targets whose BALB/c-derived non-H-2 H antigens were donated by CXB recombinant inbred mice. The spectrum of reactivity of cytotoxic effector T cells with CXB targets demonstrated that the effectors did not recognize multiple H antigens but rather preferentially recognized a single immunodominant non-H 2 antigen. The identity of the immunodominant H antigen was determined by the H-2 genotype of the stimulator cells when (B6 x B6.C-H-2d)F1 cytotoxic effectors were tested. These observations indicate that despite the fact that responders were challenged with more than 40 individual non-H-2 H antigens, they preferentially responded to single immunodominant antigen.

Medial histocompatibility antigens

Medial histocompatibility (H) antigens are weak H antigens, recognized by unrestricted T cells; they differ thus from both major and minor H antigens. An example, Qed-1, is described in detail, and other known medial H antigens of the mouse are reviewed. The structural and genetic relationships of major and medial H antigens and their role in T cell recognition are discussed.

Genetic control of B- and T-lymphocyte abnormalities of NZB mice in crosses with B10.D2 mice

Parenteral NZB and B10.D2, F1 and F1 x B10.D2 mice were studied to determine the genetic control of (1) altered B-cell IgD expression, (2) plasma cell frequency, (3) IgM secretion per plasma cell, (4) primary in vitro cytotoxic T-cell responses to H-2-compatible cells, (5) production of thymocyte-binding antibodies, and (6) production of red-cell-specific antibodies. The results demonstrate that, in this cross, IgD abnormalities and production of red-cell-specific antibodies were recessive traits. There was a common genetic influence on plasma cell frequency, IgM secretion per plasma cell and production of thymocyte-binding antibodies which was distinct from the genes governing the ability to generate a cytotoxic T lymphocyte response to H-2-compatible cells.

Leukemia-cell rejection due to T-region encoded antigens

The role of H-2- and T-region products in determining allogeneic cell rejection was evaluated in H-2 congenic and recombinant mice by transplanting A1ATH and A6ATL leukemia cell lines induced in A.TH and A.TL strains, respectively, by Moloney murine leukemia virus.--In K- or D-region incompatible hosts transplant failure was observed, while in I + T-region incompatible hosts either rejection or prolonged survival was seen. In mice preimmunized with spleen cells from I- and/or T-region incompatible donors, leukemia cells were rejected by mice immune only to T-region products, and accepted by mice immune only to I-region products.--Cell-mediated cytotoxicity studies confirmed in vivo results. Secondary CTLs specifically directed against I-region products did not lyse the A1ATH and A6ATL cells, and secondary CTLs from A.TH and A.TL mice sensitized against A6ATL and A1ATH cells respectively exerted a lytic action specific for T-region products, while no activity was observed against I determinants.--The data suggest that tumor-transplant rejection may also be governed by histocompatibility antigens encoded in the T region.

New complexities at the Qa-1 locus

Mouse strain and tissue distribution analyses indicate that the new antiserum A anti-A-Tlab recognizes the cell-surface product governed by the previously serologically undetectable Qa-1b allele. This cell-surface product has therefore been called Qa-1.2. Three levels of anti-Qa-1.2 cytotoxicity in the presence of complement have been observed: high, intermediate, and zero lysis. In general, high levels of lysis correlate with the presence of the Qa-1b allele, while zero levels of lysis correlate with the presence of the Qa-1a allele. The A.CA strain reacts with both anti-Qa-1.1 and anti-Qa-1.2 and may possess a third allele, Qa-Id. Several strains including B6-H-2k react in an intermediate fashion. Recombinant strain analyses indicate that this intermediate reaction may be due to modifying genes within the H-2D region.

Expression of the I-E target antigen for T-cell killing requires two genes

The H-2Ik region encodes at least two different target antigens for unrestricted T-cell mediated killing. The first is controlled by the I-A region alone and the second depends on a pair of alleles, one located to the left of I-B (presumably in I-A) and the other to the right of I-J (presumably in I-E). Hence, effector cells nominally specific for a product of the I-E region do not kill target cells with the same I-E region as the stimulator unless the I-A region is also shared. Some effectors specific for H-2Ik, such as A.TH anti-A.TL and B10.A(4R) anti-B10.A(2R), cross-react with B10.A(3R) and B10.A(5R) target cells. A product of the H-2b haplotype was shown to complement products of the H-2d or H-2k haplotypes in forming this cross-reactive determinant. The results are consistent with recent biochemical data on the component chains of Ia antigens.

Maternally transmitted target antigen for unrestricted killing by NZB T lymphocytes

A new target antigen for unrestricted killing was defined by NZB T lymphocytes which were immunized and restimulated with H-2-identical BALB/c spleen cells. These effector cells killed nearly all target cells tested, irrespective of their H-2 type, but did not kill NZB target cells. The response was shown to have three major components: unrestricted killing specific for Qed-1b, H-2d-restricted killing specific for minor histocompatibility antigens, and unrestricted killing specific for a new antigen, Mta. Mta is present on normal and mitogen-stimulated T and B lymphocytes and on several tumor lines. It was found on cells from 26 mouse strains tested, including two substrains of NZB, representing 9 different H-2 types and 14 different non-H-2 backgrounds. Analysis of the NX8 recombinant inbred lines (derived from Mta-NZB/Icr and Mta+C58/J parents) suggested that Mta is maternally transmitted. This was confirmed by typing of reciprocal F1 hybrids and backcrosses between positive and negative strains: Mta+ females bear Mta+ offspring and Mta- females Mta- offspring, irrespective of the phenotype of the males.