Differential induction of H-2K vs H-2D class I major histocompatibility complex antigen expression by murine recombinant interferon-gamma

The results presented here indicate that recombinant murine interferon-gamma can cause a dramatic differential induction of two distinct class I MHC molecules. Thus, IFN-gamma treatment of the murine leukemia virus (MuLV)-induced AKR SL3 tumor, a cell line that normally expresses moderate levels of class I MHC antigens, resulted in a large increase in H-2Dk expression, but no change or a slight decrease in H-2Kk expression as measured by cytofluorography. Explanations of the selective enhancement of Dk expression based on increased Fc receptor display or differential kinetics of induction were ruled out. The phenomenon was observed over a wide range of doses of IFN-gamma and with two different monoclonal antibodies to Kk, the latter finding making it unlikely that an altered form of the Kk molecule was induced. The same differential induction of the Dk antigen was observed for the LBRM.5A4 tumor cell line. Because LBRM.5A4 is also MuLV+ but of congenic B10.BR (H-2k) origin, these results were consistent with the possibility that such differential induction was associated with the H-2k haplotype and/or MuLV. The implications of these results, as a possible mechanism of tumor cell escape from an immune surveillance system monitored by class I MHC-restricted T cells and as a useful model system to dissect the mechanism of IFN-gamma induction of class I MHC antigens, are discussed.     

Interferon-gamma, interferon-alpha/beta, and tumor necrosis factor differentially affect major histocompatibility complex class I expression in murine leukemia virus-induced tumor cell lines

Tumor cell lines induced by Gross murine leukemia virus were examined for cell-surface major histocompatibility complex class I expression. Three of five cell lines constitutively express H-2K and H-2D class I protein. Culturing these cells with interferon (IFN)-gamma, IFN-alpha/beta, or tumor necrosis factor increases both K and D expression in these cell lines. Two of five tumor cell lines express no class I proteins by fluorescence-activated cell sorter analysis, specific immunoprecipitation, and specific hybridization in Northern analysis. Treatment with IFN-gamma induces D, but not K protein expression in one of these cell lines. IFN-alpha/beta and tumor necrosis factor induce neither D nor K expression in this cell line. Thus, these two cytokines appear to have different mechanisms of action than IFN-gamma for altering class I expression. The other class I-negative tumor cell line does not express either K or D proteins under any conditions tested. All five cell lines express beta 2-microglobulin; this expression is increased by IFN-gamma treatment even in cell lines which do not express class I heavy chain. The results of this study demonstrate that 1) different tumor cell lines demonstrate variations in class I gene regulation, and 2) differences in regulation between class I genes may occur within a single cell line.     

Molecular analysis of deficient class I H-2 antigen expression by mouse lung carcinoma cells

We have continued our investigations of line lung carcinoma cells to understand the molecular basis of decreased expression of class I H-2 Ag and class I Ag induction with DMSO. We show that line 1, a murine lung carcinoma cell line, has low levels of class I Ag (H-2K, D, and L) because it is deficient in both class I and beta 2-microglobulin (B2M) RNA, and that these mRNA can be coordinately induced with DMSO. Evidence presented herein also shows that IFN-gamma can induce surface expression of class I Ag and suggests that it may act through a different mechanism than DMSO in inducing class I Ag. To further evaluate the regulation of class I expression, H-2Dp genes were transfected into line 1 cells. The transfected H-2 genes appear to be constitutively expressed at much higher levels than are the endogenous class I genes because surface expression of the foreign Dp Ag on the transfectants is elevated relative to the endogenous H-2d haplotype class I Ag. Both Dp surface expression and Dp mRNA are induced after treatment with DMSO. In all the Dp transfectants, we observed higher constitutive levels of class I mRNA as well as increased constitutive levels of endogenous B2M mRNA when compared to control or untransfected line 1 cells, however, we could not correlate these constitutive levels with Dp copy number. These results suggest that the regulation of class I and B2M genes is linked and that expression of class I genes can affect the expression of B2M genes.     

Astrocytes produce interferon that enhances the expression of H-2 antigens on a subpopulation of brain cells

Using primary culture methods, we show that purified astrocytes from embryonic mouse or rat central nervous system (CNS) can be induced to produce interferon (IFN) activity when pretreated with a standard IFN-superinducing regimen of polyribonucleotide, cycloheximide, and actinomycin D, whereas IFN activity was not inducible in neuronal cultures derived from mouse CNS. Astrocyte IFN displays inductive, kinetic, physicochemical, and antigenic properties similar to those of IFN-alpha/beta, but is dissimilar to lymphocyte IFN (IFN-gamma). Treatment of pure astrocytic cultures or astrocytes cultured with neurons with astrocyte IFN or IFN-alpha/beta induced a dramatic increase in the expression of H-2 antigens on a subpopulation of astrocytes. Neither neurons nor oligodendroglia expressed detectable levels of H-2 antigens when exposed to astrocyte IFN, IFN-alpha/beta, or to IFN-beta. Injection of astrocyte IFN or IFN-alpha/beta directly into brains of newborn mice indicated that H-2 antigens were also induced in vivo. None of the IFNs (astrocyte, alpha/beta, or beta) tested induced Ia antigens on CNS cells in vitro or in vivo. Since H-2 antigens have a critical role in immune responses, astrocyte IFN may initiate and participate in immune reactions that contribute to immunoprotective and immunopathological responses in the CNS.     

Differential responses of rat trophoblast cells and embryonic fibroblasts to cytokines that regulate proliferation and class I MHC antigen expression

TNF-alpha and type I IFN (IFN-alpha/beta) are present in the uteroplacental unit during the course of normal gestation. IFN-gamma is likely to be present during infections. To identify potential effects on two types of blastocyst-derived cells, TNF-alpha, IFN-alpha/beta, and IFN-gamma were tested for the ability to modulate proliferation and the expression of class I MHC Ag by rat trophoblast cells and embryonic fibroblasts. The three cytokines had opposite influences on cellular proliferation by the two types of cells. Growth of the trophoblast cells was inhibited by TNF-alpha, IFN-alpha/beta, and IFN-gamma, whereas both TNF-alpha and IFN-alpha/beta enhanced fibroblast proliferation. The two endogenous cytokines had different effects on class I Ag expression by trophoblast cells and fibroblasts: TNF-alpha failed to induce trophoblast cell class I Ag and IFN-alpha/beta was a poor inducer whereas fibroblast Ag were induced by both cytokines. Moreover, combinations of TNF-alpha and IFN did not increase trophoblast cell class I Ag whereas the same combinations synergized to induce class I Ag expression by fibroblasts. In contrast, IFN-gamma was a highly efficient inducer on both types of cells. The results suggest that 1) cytokines in the uteroplacental unit may orchestrate some of the events associated with placental and embryonic development by exerting differential effects on two embryologically distinct types of cells and that 2) infections may disrupt normal events.     

H-2 antigen variants in a cultured heterozygous mouse leukemia cell line

An (H-2k/H-2d)F1 sarcoma cell line was subjected to immunoselection using ascites fluid from a mouse growing a hybridoma secreting an anti H-2Kk antibody.One hundred random clones were picked from the surviving population and screened by direct cytolysis using the hybridoma antibody or alloantisera against H-2Kk and H-2Dk. Fifty-nine clones were resistant to all three antisera, indicating that they no longer expressed the entire H-2k haplotype. Thirty-two were resistant to the ascites and to the anti H-2Kk alloantiserum, but sensitive to the anti H-2Dk serum, indicating that they had lost H-2Kk antigen, but retained H-2Dk. Nine clones were sensitive to the alloantisera, but resistant to the hybridoma, indicating that, though they retained the product(s) recognized by the alloantiserum against H-2Kk, they had lost the site(s) that bound the hybridoma antibody. Quantitative absorption assays using lymph-node cells from young BALB.K (H-2Kk) mice as targets show that one representative clone from the last group absorbs the anti H-2Kk activity in the alloantiserum. This implies that the sensitivity of the variant clone to the alloantiserum is not due to contaminating anti C-type virus antibodies in the serum. The possible implications of these data are discussed.     

DNA sequence analysis of the C3H H-2Kk and H-2Dk loci. Evolutionary relationships to H-2 genes from four other mouse strains

We generated nucleotide sequences for H-2Kk and H-2Dk from the C3H mouse, as well as for a genomic clone of H-2Db, in order to conduct an evolutionary analysis of the H-2 genes from three haplotypes, k, d, and b. H-2Kk from both the C3H and AKR strains, H-2Kd, H-2Kb, H-2Dk, H-2Ld, H-2Dd, H-2Db, and H-2Dp DNA sequences were aligned, and the alignments used to construct phylogenetic trees inferring the evolutionary relationships among the nine genes by two independent methods. Both approaches yielded trees with similar topologies. In addition, the sequence alignments revealed patterns of nucleotide substitutions which implicate both point mutation and recombination in the divergence of the H-2 genes. Future considerations for evolutionary analysis of class I genes are discussed.     

Deficient major histocompatibility complex-linked innate murine cytomegalovirus immunity in MA/My.L-H2b mice and viral downregulation of H-2k class I proteins

NK cells are key effectors of innate immunity and host survival during cytomegalovirus (CMV) infection. Innate murine CMV (MCMV) resistance in MA/My mice requires Ly49H/m157-independent H-2k-linked NK cell control. Here we show that replacement of MA/My H-2k with C57L H-2b susceptibility genes led to a remarkable loss of innate virus immunity, though NK gamma interferon was induced in H-2b and H-2k strains shortly after infection. Thus, H-2b genes expressed in C57L or MA/My.L-H2b are sufficient in alerting NK cells to intrusion but fail to support NK restraint of viral infection. In addition, novel H-2 recombinant strains were produced and utilized in a further refinement of a critical genetic interval controlling innate H-2k-linked MCMV resistance. Importantly, this analysis excluded the gene interval from Kk class I through class II. The responsible gene(s) therefore resides in an interval spanning Dk class Ia and more-distal major histocompatibility complex (MHC) nonclassical class Ib genes. Recently, the NK activation receptor Ly49P and MHC class I Dk proteins were genetically implicated in MCMV resistance, in part because Ly49P-expressing reporter T cells could specifically bind Dk molecules on MCMV-infected mouse embryonic fibroblasts (MEFs). However, as we found that H-2k innate resistance differs in the C57L or MA/My backgrounds and because MCMV very efficiently downregulates H-2k class I proteins in L929 cells and primary MEFs shortly after infection, a Ly49P/Dk model should not fully explain H-2k-linked MCMV resistance.     

Differential regulation of Dk and Kk major histocompatibility complex class I proteins on the cell surface after infection of murine cells by pseudorabies virus.

After pseudorabies virus (PRV) infection of murine L929 cells, the cell surface expression of major histocompatibility complex (MHC) class I proteins changes such that the total amount of MHC class I molecules remains relatively constant but the levels of the individual alleles Dk and Kk vary. This is an active process involving at least three PRV gene products that act in an allele-specific manner such that cell surface expression of MHC class I Dk is decreased and that of Kk is increased. Our results indicate that an early gene product mediates the overall reduction in Dk protein and a late gene product which is mutant in the attenuated PRV strain Bartha mediates the increase in Kk protein. We provide additional evidence for a third gene product involved in the regulation of the synthesis of both the Dk and Kk proteins. In addition, we show that the early decrease in the Dk protein is not due to a block in synthesis or processing of the complex through the secretory system.     

Dual parameter, quantitative cytofluorometric analysis of endogenous H-2Kk and foreign HLA class I molecules expressed at the surface of murine transformed L cells

By using a calibrated dual laser cell sorter and monoclonal antibodies directly conjugated to fluorescein and rhodamine and specific for H-2Kk and HLA class I antigens, quantitative cytofluorometric analysis was performed on individual HLA-A3 or -CW3 transformed mouse L cells (H-2k). More than 80% of these cells expressed both HLA class I and H-2Kk molecules. Their respective levels of expression were calculated: a mean of 4 X 10(5) HLA class I and 2.3 X 10(5) H-2Kk molecules per single cell. Quantitative comparison with control untransformed L cells and double fluorescence contour maps showed a positive correlation between the levels of expression of HLA class I and H-2Kk molecules suggesting that expression of foreign class I molecules did not occur at the expense of the endogenous H-2k product.     

Inability of mice to generate cytotoxic T lymphocytes to vesicular stomatitis virus restricted to H-2Kk or H-2Dk

H-2k mice are unable to generate cytotoxic T lymphocytes (CTL) to vesicular stomatitis virus (VSV). This apparent unresponsiveness is found for both major serotypes of VSV, VSV-Indiana and VSV-New Jersey. CTL unresponsiveness occurs despite the ability of H-2k mice to generate a humoral immune response against VSV that is comparable to that found in responder (H-2b and H-2a) strains. All H-2k mice regardless of background genes, including various Ig allotypes, were found to be nonresponders. H-2k-linked unresponsiveness mapped to both H-2Kk and H-2Dk and occurred despite the presence of responder alleles in (responder x nonresponder)F1 mice. The unresponsiveness cannot be attributed to an inability of VSV-infected H-2k target cells to express viral surface antigens of H-2 molecules. Further, unresponsiveness cannot be overcome by using secondary stimulation in vivo or in vitro. H-2k-linked unresponsiveness does not appear to be due to suppression, and no complementation has been found in various (nonresponder x nonresponder)F1 mice. Thus unresponsiveness to VSV in association with H-2Kk or H-2Dk appears to represent an extensive defect of immune responsiveness that probably occurs because VSV is not a natural mouse pathogen.     

Transfection of beta 2-microglobulin restores IFN-mediated protection from natural killer cell lysis in YAC-1 lymphoma variants

A beta 2-microglobulin (beta 2m)-deficient variant of YAC-1, A.H-2-, was transfected with a genomic beta 2m clone. Transfected cells were used to investigate the role of beta 2m in IFN-induced protection from NK cell lysis. IFN-gamma treatment of the NK-sensitive murine YAC-1 lymphoma results in reduced sensitivity to NK cell-mediated lysis in parallel with increased expression of its constitutively low MHC class I expression. It was previously shown that the A.H-2- variant had lost both these capacities, although it retained other responses to IFN-gamma. Here beta 2m transfection restored the YAC-1 phenotype with respect to an inducible expression of MHC class I molecules and a concomitant protection from NK cell lysis after treatment with IFN-gamma. In the absence of IFN-gamma the NK sensitivity of the transfectants did not differ significantly from A.H-2-. A similar protection from NK cell lysis, in parallel with enhanced MHC class I expression, was observed for in vivo-passaged beta 2m transfectants whereas no protection was found for in vivo-passaged A.H-2- cells. The present study provides evidence that the IFN-gamma-mediated protection from NK cell lysis is dependent on beta 2m expression in the YAC-1 lymphoma. Restoration of MHC class I assembly, transport, and concomitantly an IFN-gamma augmentable cell surface expression of MHC class I molecules is a possible explanation for the effect of beta 2m.     

Somatic variation of H-2Kk expression and structure in a T-cell lymphoma: instability, stabilization, high production and structural mutation

In the heterozygous T lymphoma line LDHB, variants which have lost the expression of individual H-2 class I genes are spontaneously generated in vitro at a frequency of 10(-1)-10(-2). A cell line (HK13) in which the class I gene Kk is stably expressed (frequency of loss variants less than 10(-4) was selected from LDHB cells by fluorescence activated cell sorting. Further selection of HK13 cells for high Kk expression led to the isolation of the HK22 line which expresses twice as much Kk as HK13. From HK13 and HK22 cells, spontaneous structural variants of Kk having lost individual serological determinants of the Kk wild-type molecule, were isolated by fluorescence activated cell sorting. Such variants occur at a frequency of 10(-6)-10(-7) per cell per generation. The analysis of these variants indicates that they carry mutations in the Kk structural gene and that HK13 cells express a single Kk gene which appears to be duplicated in HK22 cells. We did not find evidence for the generation of variants expressing 'alien' class I products in the LDHB cell line. The instability of class I gene expression in LDHB cells and the transition to stable expression may represent steps of T-cell differentiation in the thymus.     

Intracellular transport of membrane glycoproteins: two closely related histocompatibility antigens differ in their rates of transit to the cell surface

The intracellular transport of two closely related membrane glycoproteins was studied in the murine B cell lymphoma line, AKTB-1b. Using pulse-chase radiolabeling, the kinetics of appearance of the class I histocompatibility antigens, H-2Kk and H-2Dk, at the cell surface were compared and found to be remarkably different. Newly synthesized H-2Kk is transported rapidly such that all radiolabeled molecules reach the surface within 1 h. In contrast, the H-2Dk antigen is transported slowly with a half-time of 4-5 h. The rates of surface appearance for the two antigens closely resemble the rates at which their Asn-linked oligosaccharides mature from endoglucosaminidase H (endo H)-sensitive to endo H-resistant forms, a process that occurs in the Golgi apparatus. This suggests that the rate-limiting step in the transport of H-2Dk to the cell surface occurs before the formation of endo H-resistant oligosaccharides in the Golgi apparatus. Subcellular fractionation experiments confirmed this conclusion by identifying the endoplasmic reticulum (ER) as the site where the H-2Dk antigen accumulates. The retention of this glycoprotein in the ER does not appear to be due to a lack of solubility or an inability of the H-2Dk heavy chain to associate with beta 2-microglobulin. Our data is inconsistent with a passive membrane flow mechanism for the intracellular transport of membrane glycoproteins. Rather, it suggests that one or more receptors localized to the ER membrane may mediate the selective transport of membrane glycoproteins out of the ER to the Golgi apparatus. The fact that H-2Kk and H-2Dk are highly homologous (greater than or equal to 80%) indicates that this process can be strongly influenced by limited alterations in protein structure.