Medial histocompatibility antigens

The selection of M3-restricted T cells is dependent on M3 expression and presentation of N-formylated peptides in the thymus

The major histocompatibility complex (MHC) class Ib molecule H2-M3 binds N-formylated peptides from mitochondria and bacteria. To explore the role of M3 expression and peptide supply in positive and negative selection, we generated transgenic mice expressing an M3-restricted TCR-alpha/beta from a CD8(+) T cell hybridoma (D7) specific for a listerial peptide (LemA). Development of M3-restricted transgenic T cells is impaired in both beta2-microglobulin-deficient and transporter associated with antigen processing (TAP)-deficient mice, but is not diminished by changes in the H-2 haplotype. Maturation of M3/LemA-specific CD8(+) single positive cells in fetal thymic organ culture was sensitive to M3 expression levels as determined by antibody blocking and use of the castaneus mutant allele of M3. Positive selection was rescued in TAP(-/-) lobes by nonagonist mitochondrial and bacterial peptides, whereas LemA and a partial agonist variant caused negative selection. Thus, M3-restricted CD8(+) T cells are positively and negatively selected by M3, with no contribution from the more abundant class Ia molecules. These results demonstrate that class Ib molecules can function in thymic education like class Ia molecules, despite limited ligand diversity and low levels of expression.

Positive selection of an H2-M3 restricted T cell receptor

Thymocytes are positively selected for alphabeta T cell antigen receptors (TCR) that recognize antigen in conjunction with self-major histocompatibility complex (MHC) molecules. MHC bound peptides participate in positive selection; however, their role has remained controversial. A TCR transgenic mouse was established using a TCR restricted to the MHC class Ib molecule, H2-M3. Having defined H2-M3 as the positively selecting MHC molecule, the severely limited number of H2-M3 binding peptides allowed us to characterize an NADH dehydrogenase subunit 1 (ND1)-derived peptide as the physiological ligand of positive selection. This peptide bears no apparent sequence homology to the cognate peptide, is expressed ubiquitously, and yet does not interfere with peripheral T cells. Our studies also suggest that positive selection becomes promiscuous at high epitope densities.

Transporters associated with antigen processing (TAP)-independent presentation of soluble insulin to alpha/beta T cells by the class Ib gene product, Qa-1(b)

T cell hybridomas isolated from nonresponder H-2(b) mice immunized with pork insulin were stimulated by insulin in the presence of major histocompatibility complex (MHC)-unmatched antigen presenting cells. The restriction element used by these CD4(-) T cells was mapped to an oligomorphic MHC class Ib protein encoded in the T region and identified as Qa-1(b) using transfectants. The antigenic determinant was localized to the insulin B chain, and experiments with truncated peptides suggested that it is unexpectedly long, comprising most or all of the 30 amino acid B chain. The antigen processing pathway used to present insulin to the Qa-1(b)- restricted T cells does not require transporters associated with antigen processing (TAP), and it is inhibited by chloroquine. A wide variety of cell lines from different tissues efficiently present soluble insulin to Qa-1(b)-restricted T cells, and insulin presentation is not enhanced by phagocytic stimuli. Our results demonstrate that Qa-1(b) can function to present exogenous protein to T cells in a manner similar to MHC class II molecules. Therefore, this class Ib protein may have access to a novel antigen processing pathway that is not available to class Ia molecules.

The class I-b molecule Qa-1 forms heterodimers with H-2Ld and a novel 50-kD glycoprotein encoded centromeric to I-E beta

Recent biochemical characterization of the T23-encoded Qa-1 molecule revealed an additional higher molecular mass species of 50 kD coprecipitated with the 48-kD Qa-1 molecule in H-2b and H-2d mouse strains. We now demonstrate that the 50-kD protein coprecipitated with Qa-1 is the class I-a antigen Ld in all H-2Ld-positive mouse strains examined. Furthers analyses of a panel of recombinants revealed that the 50-kD protein coprecipitated with Qa-1 in H-2b haplotype mouse strains is encoded or controlled by a gene centromeric to major histocompatibility complex class II I-E beta. We have designated this gene and corresponding protein product as Qsm, Qa-1 structure modifier. Both Ld and Qsm can interact with Qa-1 to form cell surface-expressed heterodimers in vivo. These Qa-1 heterodimers are not expressed in H-2k haplotype cells. The Qa-1/Ld and Qa-1/Qsm heterodimers are associated by noncovalent interactions and occur only between fully processed proteins. In addition, we show that the Qsm-encoded protein can form heterodimers with Ld as well, and that the Ld molecules participating in these interactions with Qa-1 and Qsm may be devoid of beta 2-microglobulin and/or peptide. These data represent the first demonstration that class I molecules can be expressed as heterodimers (Qa-1/Ld) on the cell surface, and map a gene (Qsm) that may potentially encode a novel class I molecule, or another protein, that associates with both Qa-1 and Ld. These interactions may enable increased levels of Qa-1 to reach the cell surface and may subsequently influence T cell recognition of Qa-1 and/or Ld molecules.

Organization and structure of the H-2M4-M8 class I genes in the mouse major histocompatibility complex

We have cloned and characterized five new class I genes from the M region at the distal end of the H-2 complex of the BALB/c mouse. M4, M5, and M6 are clustered on two overlapping cosmids, and M7 and M8 are located on another cosmid together with the previously cloned M1 gene, to which they are most closely related. M4, M6, and M7 are full-length class I genes (exons 1 through 5 were identified) but with stop codons or frameshifts that mark them as pseudogenes, and only exons 4 and 5 remain of M8. M5 has complete open reading frames in exons 1 through 5 and intact splice signals; it has the potential to encode a divergent class I major histocompatibility molecule, but no transcripts were found. These genes provide probes for studying the evolution of class I genes in rodents and for the mapping and cloning of genes at the end of the distal inversion in t haplotype chromosomes.

HMT, encoded by H-2M3, is a neoclassical major histocompatibility class I antigen

H-2M3 encodes HMT, the major histocompatibility complex (MHC) class I heavy chain of the maternally transmitted antigen (Mta). Like classical MHC class I genes, the expression of M3 can be stimulated by gamma-interferon and its message can be detected from mid-gestational embryos (day 8) through adulthood. HMTb, a nonimmunogenic allelic form of HMT, differs from the common HMTa molecule by four amino acids, of which only two (residues 31 and 95) are located in the alpha 1 and alpha 2 domains that form the peptide-binding groove. Recognition of site-directed mutants by Mta-specific cytotoxic T lymphocytes was hardly affected by the substitution of Met for Val31 but was abolished by the substitution of Gln for Leu95, which is located in the beta-sheet floor of the peptide-binding groove. Thus a single amino acid difference is responsible for the immunological silence of HMTb.

H-2M3 encodes the MHC class I molecule presenting the maternally transmitted antigen of the mouse

Mta, the maternally transmitted antigen of mice, is a hydrophobic, N-formylated mitochondrial peptide, MTF, presented on the cell surface to cytotoxic T lymphocytes by a novel major histocompatibility complex class I molecule, encoded by H-2M3. We have cloned and sequenced two alleles of M3, which differ in their ability to present MTF despite greater than 99% identity in the coding regions. M3 is as divergent from classical, antigen-presenting H-2 molecules as from other class I genes of the Hmt and the Qa/Tla regions. Amino acids critical for folding of class I molecules are conserved in M3. Noncharged amino acids lining the peptide-binding groove and phenylalanine 171 may explain the unique interaction with MTF, and leucine 95 appears critical for immunological activity.

Recognition of MHC TL gene products by gamma delta T cells

We have studied the ligand specificity of a gamma delta T-cell receptor (TCR) derived from a mouse T-cell hybridoma (KN6). KN6 cells reacted with syngeneic (C57BL/6) cells from various origins (splenocytes, thymocytes, peritoneal exudate cells, etc.) and cells from many different mouse strains. KN6 reactivity against cells from a panel of congenic and recombinant mouse strains demonstrated that the ligand recognized by KN6 is controlled by an MHC-linked gene that most probably maps in the TL region. We cloned this gene and formally proved that it does map in the TL region. This gene turned out to be a novel class I gene (designated T22b) belonging to a hitherto unidentified cluster of TL region genes in strain C57BL/6. This gene was expressed in many different tissues and cell types. We also examined the tissue expression of several other TL genes. One of these, the structural gene (T3b) encoding the thymus leukemia (TL) antigen from C57BL/6 mice, was specifically expressed in the epithelium of the small intestine. Since the intestinal epithelium of the mouse is known to be the homing site for a subset of gamma delta T cells (i-IEL) bearing diverse TCR with V7 rearranged gamma chains, we propose that the T3b gene product is part of the ligand recognized by some of the i-IEL. Our data support the idea that gamma delta T cells might be specific for non-classical class I or class I-like molecules and suggest that gamma delta TCR and non-classical MHC co-evolved for the recognition of a conserved set of endogenous or foreign peptides.

Generation of T cells with lytic specificity for atypical antigens. I. A mitochondrial antigen in the rat

F1 rats primed with normal parental strain lymphocyte populations and restimulated in culture with parental lymphoblasts generate potent cytotoxic T cell responses to unusual antigen systems. Here we describe in the Lewis (L)/DA anti-DA combination an antigen system most likely of mitochondrial origin with the following properties: it is transmitted maternally from DA strain females, inherited in an extra-chromosomal manner, restricted by class I RT1Aa major histocompatibility complex gene products, extinguished on target cells treated with chloramphenicol, and its pattern of expression in different rat strains correlates with restriction fragment-length polymorphisms of mitochondrial DNA. Sequence analysis of the rat ND1 gene indicates that the maternally transferred factor in the rat is not a homologue of the maternally transmitted factor responsible for the mitochondrial antigen in mice. In keeping with its inheritance from DA females, this antigen is present on target cells from (DA female x L male)F1 donors and all other F1 combinations derived from DA female parents, but absent from target cells from some F1 combinations (L/DA and Wistar-Furth [WF]/DA) derived from DA strain males. The presence of this antigen in other F1 combinations (Brown Norway [BN]/DA, August 2880 [AUG]/DA, and PVG/DA) indicates that this mitochondrial antigen system is shared by the DA, BN, and PVG strains, but not by the L and WF strains.

Variants of Mta, the mouse maternally transmitted antigen, determined by three alleles of the extrachromosomal gene Mtf

Two new forms of Mta, the maternally transmitted antigen of the mouse, were defined by cytotoxic T lymphocytes. One is found in laboratory mice carrying the beta allele of the maternally transmitted factor, Mtf, which were previously thought to be Mta-negative. The other is associated with a new allele, Mtf gamma, and is found in wild mice from Toulouse. Like the common form of Mta, determined by the extrachromosomal Mtf alpha, the new forms are also dependent on the a allele of Hmt, a chromosomal gene linked to H-2, and are associated with beta 2-microglobulin. Killers could be raised in all six combinations of alpha, beta, and gamma mice, showing that each form of Mtf determines a distinct (set of) epitope(s). We propose that the product of the Hmt gene, a class I MHC antigen, presents a peptide derived from a mitochondrial gene product on the cell surface and thereby creates the target antigen, Mta.

Regulation of Qa-1 expression and determinant modification by an H-2D-linked gene, Qdm

We examined the regulation of cell surface expression of the Qa-1 alloantigens using a panel of monoclonal anti-Qa-1 cytotoxic T-lymphocyte (mCTL) lines. In contrast to previous reports of tissue-specific expression, we found that Qa-1 was widely expressed, resembling the prototypical class I H-2K/D molecules. We further found that an H-2D-linked gene, which we termed Qdm for Qa-1 determinant modifier, controlled expression of certain CTL-defined Qa-1 antigenic determinants. H-2Dk homozygous haplotypes expressed a recessive allele of the modifier, Qdmk, whereas all other H-2 haplotypes tested expressed a dominant allele, Qdm+. The Qdm+ allele regulated in trans Qa-1 epitope expression from a Qdmk chromosome, modifying expression of particular CTL-defined Qa-1 antigenic determinants rather than affecting levels of cell surface expression. Mechanisms of Qdm function may include either a novel protein modification system or an unprecedented case of antigen recognition restricted by a nonclassical major histocompatibility complex molecule.

Interleukin 2 and its receptor: structure, function and therapeutic potential

In this review, salient molecular, biochemical and functional features of human interleukin 2 (IL-2), its membrane receptor, and its clinical relevance are outlined. We also describe experimental systems, where observed biological or pharmacological effects of IL-2 could be applied to corresponding clinical situations. In particular, IL-2 has been intensively studied in the context of cancer therapy. We discuss the rationale for the use of IL-2 in cancer treatment and our experience in this area. A better understanding of the IL-2 system and, specifically, the nature of signals transduced through it will allow us to manipulate the immune response in a variety of different ways, resulting in new approaches to investigation of immune responsiveness in general. This may have a profound impact on clinical medicine.

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.

Unglycosylated Mtaa expresses an Mtab-like determinant

Antigenic polymorphism of the class I-like maternally transmitted antigen (Mta) is controlled by a maternally transmitted factor (Mtf) thought to reside in mitochondria. However, the mechanisms by which Mtf generates antigenic polymorphism are not known. To address this issue, we investigated a possible role of posttranslational oligosaccharide addition in the formation of Mta determinants. We examined the expression of Mta on cytotoxic T lymphocyte (CTL) target cells cultured in tunicamycin (TM), a known inhibitor of asparagine(N)-linked glycosylation. Of 18 Mtab-specific CTL lines, 8 lysed TM-treated Mtaa targets. Furthermore, a subclone of one of these eight lines, 17D5.G2, lysed TM-treated targets from all Mtaa strains tested, regardless of H-2K/D haplotype. On the other hand, this CTL clone did not lyse TM-treated target cells from the Mta null, but H-2 expressing strain B10.CAS2. Therefore expression of this Mtab-like determinant is concordant with the expression of Mtaa and seems unlikely to represent a cross-reactive H-2K/D epitope. Our data suggest that an Mtab-like determinant is expressed on unglycosylated Mtaa molecules. Thus, N-linked oligosaccharides probably prevent the expression of an Mtab-like determinant on the Mtaa molecule. We discuss how Mtf may contribute to Mta polymorphism through glycosylation.

Minor but not major histocompatibility antigens of thymus epithelium tolerize precursors of cytolytic T cells

Treatment of fetal thymuses with 2-deoxyguanosine depletes these organs of many haematopoietic cells, and if such thymuses are transplanted into allogeneic athymic nude mice, intrathymic development of cytolytic T-lymphocyte precursors (CTL-P) occurs, including those which are specific for class I major histocompatibility complex (MHC) antigens expressed by the thymus epithelium. Thus, T cells from BALB/c (H-2d) nude mice transplanted with allogeneic C57BL/6 (H-2b) thymic epithelium can be stimulated in vitro to produce CTL specific for H-2b class I MHC antigens. We report here that thymocytes and lymph node T cells from such mice are responsive in mixed leukocyte reaction in the absence of exogenous growth factors, indicating that lack of tolerance is manifest at the level of CTL-P and proliferating T cells. We also show that T cells from such mice are tolerant to minor histocompatibility antigens of the thymus donor in the context of MHC antigens of the recipient. The results indicate that haematopoietic rather than epithelial cells tolerize CTL-P and that donor-type minor but not major histocompatability antigens can be presented in tolerogenic form by haematopoietic cells expressing recipient-type MHC antigens.

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.

Minor histocompatibility antigens are developmentally regulated on murine embryonal carcinoma cells and their early differentiated derivatives

Differences in the expression of minor histocompatibility (Hm) alloantigens on two mouse embryonal carcinoma (EC) cell lines and the PYS-2 and T.D.M.-1 differentiated derivatives have been demonstrated by their ability to elicit a cytolytic T lymphocyte response. Experiments involving the use of various responder-target strain combinations and recombinant inbred mice strains have shown that: (1) there are major differences in Hm expression on EC cells compared with differentiated derivatives whose Hm expression appears more like that of adult splenocytes; (2) although both EC cell lines show reduced Hm immunogenicity compared with adult splenocytes, major differences in the expression and possible presentation of Hm between the F9 and PCC3 EC cell lines can be detected by in vivo priming and by in vitro cold competition target experiments. These observations are discussed in relation to the differences in allograft rejection patterns observed with PCC3 and F9 and to possible differences in developmental staging of these cell lines.

Mitochondrial modulation of maternally transmitted antigen: analysis of cell hybrids

Maternally transmitted antigen (Mta) is a murine cell surface class I-like antigen that is defined by specific cytotoxic lymphocyte reactivity. Mta is unique in that its expression requires cooperation between genetic elements both in the Qa/Tla region of chromosome 17 and in the cytoplasm. In view of the known cytoplasmic, and thus maternal, inheritance of mitochondria, we have directly assessed their potential involvement in Mta expression. The mitochondria-specific lethal dye rhodamine 6G (R6G) was used to control the input of mitochondria into cell hybrids. The parental lines, one of BALB/c and one of NZB origin, were known to differ in Mta and mtDNA phenotype. Our data show that most control BALB/c-NZB hybrids expressed the BALB/c Mta phenotype and likewise contained only BALB/c-type mtDNA. The NZB Mta phenotype was not coexpressed in the control hybrids. However, when the mitochondrial contribution from BALB/c was prevented by R6G treatment, the majority of the resultant hybrids expressed only the NZB Mta type and likewise contained only NZB mtDNA. The exceptional R6G-treated hybrids that continued to express the BALB/c Mta phenotype likewise contained only BALB/c mtDNA. Thus, in every case the mtDNA phenotype correlated with the Mta phenotype of the cells. Together, the data support the remarkable conclusion that mitochondria modulate the phenotypic expression of a cell surface molecule.

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.

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.

Naturally occurring spleen-associated suppressor activity of the newborn mouse. Requirement for two genetic restrictions in suppression of lethal graft-versus-host disease by newborn spleen cells

Spleens from newborn mice less than 6-7 days of age are known to contain naturally occurring suppressor cells, which can suppress the immune reactivity of third-party adult cells. In the present study newborn spleen cell populations are shown to possess the potential to inhibit lethal graft-versus-host (GVH) disease in sublethally gamma-irradiated hosts injected with allogeneic adult cells. However, this capacity to suppress GVH disease is controlled by at least two genetic restrictions: (1) the newborn spleen cells and the adult donor cells must be histocompatible at an H-2-linked region apparently telomeric of H-2DL, and (2) the newborn spleen cells must express a strongly stimulating non-H-2 (perhaps M1s) alloantigenic phenotype. Host animals that survive GVH remain chimeric for at least 3-4 weeks but return to the host phenotype by 8-10 weeks. Thus, it appears that in sublethally irradiated hosts the newborn cells suppress donor cell reactivity long enough for the host system to recover from the effects of irradiation.

Mitochondria control expression of a murine cell surface antigen

Maternally transmitted antigen (Mta) is a murine cell-surface molecule defined by the reactivity of specific H-2 nonrestricted cytotoxic T lymphocytes (CTL-s). Maternal transmission appears to be under control of a stable genetic factor in the cytoplasm of the ovum. In view of the known maternal inheritance of mitochondria we have assessed their involvement in Mta expression using the mitochondria specific poison Rhodamine 6G (R6G). We report here that Mta expression in somatic cell hybrids requires functional mitochondria from the Mta+ parent cell line. Mta expression was dominant in hybrids from the fusion of Mta+ and Mta- cells. However, pretreatment of the Mta+ parent with R6G resulted in hybrids which were Mta-, or diminished in Mta expression. These data strongly implicate mitochondrial DNA (mtDNA) in the expression of a cell-surface molecule, and define a system for studying a previously unrecognized mitochondrial function. To our knowledge, this is the first evidence for mitochondrial control of the expression of a cell membrane molecule in eukaryotes.

A new H-2-linked class I gene whose expression depends on a maternally inherited factor

The maternally transmitted antigen (Mta) is expressed on the cells of most strains of mice. It is a medial histocompatibility antigen, that is, it is recognized by unrestricted cytotoxic T lymphocytes as are major H antigens, but unlike these it is a weak transplantation antigen and does not itself restrict the T-cell recognition of minor H antigens. All other medial H antigens are encoded by genes closely linked to the major histocompatibility complex, H-2 in the mouse. By contrast, Mta appeared to follow extrachromosomal, maternal inheritance. Several substrains of NZB, NZO and non-inbred European NMRI mice are Mta-negative. Females of these strains bear only Mta- offspring, while females of the inbred Mta+ strains bear only Mta+ offspring. Repeated backcrossing from Mta+ females to NZB or NMRI males has shown that, given the right cytoplasmic genes, the chromosomal genes of these Mta- strains permit expression of Mta2. As the Mta type of a mouse cannot be influenced by embryo transfer or foster nursing, we concluded that it was determined by a cytoplasmic factor (Mtf), transmitted through the egg. We now show that a gene, Hmt, closely linked to the H-2 complex, is also required for expression of Mta.

The major histocompatibility complex of the rat: a partial review

The major histocompatibility complex of the rat is now called RT1, and this name is becoming widely accepted. In the past five years many recombinants have been reported within RT1 that enable distinct functional regions to be identified and located relative to each other. RT1 does not at present look particularly like its closest known relative, H-2. No doubt the genetic relationship will become apparent at the DNA level. The spontaneous diabetes mellitus of the BB rat line is associated with RT1. The data so far suggest that RT1u supplies a dominant susceptibility that becomes apparent only if protection conferred by a dominant gene mapping outside the MHC is withdrawn. It seems likely that the BB rat carries a recessive mutation at this "protective" locus.

Differences in maternal lineages of New Zealand Black mice defined by restriction endonuclease analysis of mitochondrial DNA and by expression of maternally transmitted antigen

Two substrains of New Zealand Black (NZB) mice have been compared with respect to expression of a maternally transmitted cell surface antigen, Mta, defined by cloned cytolytic T cells, and for restriction enzyme polymorphisms of mitochondrial DNA (mtDNA). These independent assays of maternal cytoplasmic inheritance provide strong evidence for genetic contamination of the NZB/BlPt substrain (NZB/Bl mice from Michael Potter's separate colony at the National Institutes of Health), in which the typical NZB immunologic abnormalities are at least partially ameliorated. The decisive data are the restriction enzyme maps of mtDNA for NZB/BlPt, which were identical with those of the common "old inbred" strains and quite different from those of NZB/BlN (NZB/Bl mice from the breeding facility at the National Institutes of Health). It is probable that the contamination of the NZB/BlPt substrain is related to phenotypic changes in their autoimmune state. More interestingly, the data are consistent with, although they do not prove, involvement of the mitochondrial genome in expression of a cell surface molecule.

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.