High titres of antibody to murine leukaemia virus in lymphocyte (Ly) alloantisera

Anti-nuclear antibodies in murine alloantisera are not necessarily related to antibodies to murine leukemia viruses

Murine alloantisera often contain antinuclear antibodies. Frequently, these sera also have antibodies to murine leukemia viruses. In order to evaluate the relationship of these activities several alloantisera were tested for the presence of antinuclear and antiviral antibodies. The results of this study show that there is neither quantitative nor qualitative correlation between antinuclear and antiviral antibodies.

Ly- and ecotropic MuLV antigens are separate entities

Murine alloantisera to lymphocyte (Ly) alloantigens also contain antibodies to murine leukaemia viruses (MuLV) in high titre. A number of such sera were extensively absorbed with ecotropic AKR murine leukaemia virus to remove contaminating anti-MuLV antibodies. The virus-absorbed and unabsorbed antisera were then examined by the radioimmune precipitation (RIP) assay for anti-MuLV antibodies, and for anti-Ly antibodies by cytotoxicity assays against specific target cells. The results presented here demonstrate that whilst virus absorption markedly reduced the anti-viral titres of the alloantisera they had no effect on the anti-Ly titres of any of them. This indicates that none of the Ly antigens which was examined cross reacts with the antigens of ecotropic AKR-MuLV and further suggests that Ly antigens are not encoded by the genes of endogenous ecotropic MuLVs. It was also demonstrated that the majority of the contaminating anti-MuLV antibodies present in anti-Ly-6.2 antiserum recognize viral envelope antigens rather than the internal structural proteins of the virus.

Description of a Qa-2 like alloantigen (Qa-m2)

Several new aspects of the chemistry, genetics and cellular distribution of the murine Qa-2 alloantigen were apparent in an analysis of this antigen using monoclonal antibodies recognizing a Qa-2-like antigen called Qa-m2. Immunoprecipitation and sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis identified the Qa-m2 alloantigen as a two-chain structure composed of a 39 000 dalton heavy chain and a 12 000 light chain which is probably beta 2-microglobulin; the heavy chain was readily distinguished from that of H-2. In addition, the expression of Qa-m2 alloantigens on the cell surface was found to be controlled by the H-2D gen with H-2Db strains carrying approximately 8-10 times greater amounts of Qa-m2 than strains carrying the H-2Dd or H-2Dq alleles. Finally, the Qa-m2 antigen, found predominantly on peripheral T cells, was present on only 10% of thymus cells. However, subpopulations of B cells (approximately 25% of all B cells) and bone marrow cells (15-20%) were also reactive. The monoclonal anti-Qa-m2 antibodies differed in their reactions from that reported for the conventional anti-Qa-2 sera, which must, therefore, be complex. The monoclonal antibodies may be useful reagents for functional analysis of T and B cell subpopulations.

Lym 7.2: monoclonal antibody defining an alloantigen similar or identical to Ly 7.2

Immunization of B10.D2 Ign mice against a (BALB/c X NZB)F1 murine B lymphoma cell line (WEHI-5) and subsequent fusion of immune spleen cells with a drug sensitive myeloma (P3 X 63-Ag8) has resulted in the generation of a series of hybridoma cell lines. One of these clones, BD5-334.5, secretes an antibody which reacts with a determinant, designated Lym 7.2, which demonstrates an identical tissue and strain distribution as the conventionally defined Ly 7.2 antigen. Furthermore, anti-Ly 7.2 alloantiserum significantly blocks reaction of the anti-Lym 7.2 monoclonal antibody with BALB/c splenocytes. Lym 7.2 is present on a majority of splenocytes, peripheral blood leukocytes, and lymph node cells. However, B cells express considerably higher cell surface density of this antigen than peripheral T lymphocytes. This antigen was not detected on erythrocytes, kidney, liver, or brain. Moreover, Lym 7.2 is present on approximately 15% of normal thymocytes, and 15% of bone marrow cells, and is expressed on cortisone resistant thymocytes. Quantitative flow cytometry analysis demonstrated that the antigen is present at approximately half the cell surface density on spleen cells from F1 mice between Lym 7.2 positive and Lym 7.2 negative mice, but on the same percentage of cells as Lym 7.2 positive inbred strains. Data from backcross analysis suggest that a single locus is encoding this antigen. Mitogen blasts, induced with PHA, ConA, and LPS, all express the Lym 7.2 marker.

Evidence for expression of Ly-6.2 on non-bone marrow-derived cells in kidney, skin and connective tissues

Mouse alloantigen Ly-6.2 is detectable in various non-lymphoid tissues such as kidney, but it is not clear whether or not this expression is due to bone-marrow derived passenger leukocytes. To determine whether non-marrow derived cells express Ly-6.2, we examined the expression of this antigen in kidney and on isolated connective tissue and epidermal cells. Studies in radiation chimeras demonstrated that the kidney did not become Ly-6.2 positive when negative animals were reconstituted with positive marrow. Thus, passenger leukocytes cannot account for the renal expression of Ly-6.2, indicating that most of this antigen is on non-marrow-derived (parenchymal) cells in kidney. Various isolated cell types--fibroblasts, osteocytes, chondrocytes and skin epidermal cells--were found to be Ly-6.2 positive. Indeed, absorption and cytotoxicity results suggested that the amount of Ly-6.2 on fibroblasts exceeded the amount of an H-2 antigen on these cells. Comparison of fibroblasts to lymphocytes indicated that fibroblasts had 13--60 times more Ly-6.2 than spleen cells and three times more than PHA blasts. The results indicate that the Ly-6.2 detected in non-lymphoid tissues is predominantly on the parenchymal or connective tissue elements of those tissues.

Antinuclear factors in murine alloantisera

We have demonstrated that anti-Thy 1.1 and certain of H-2 alloantisera contain an antinuclear factor (ANF) detected by fluorescent antimouse IgG. The incidence of ANF positive antisera that we report may actually be an underestimate. ANF is present in sera not only from our laboratory but also from other sources; thus ANF is not an artifact of our laboratory. ANF is not identical to alloantibody, and the ANF appears to be of an autoimmune nature. A variety of environmental and genetic factors may influence the appearance of ANF in anti-H-2 sera, but we believe that the consistent detection of ANF in sera directed against H-2.31,34 or against H-2.4 suggest that some specific aspect of immune stimulation by these H-2 antigens, and likely by other H-2 antigenic specifications, induces the appearance of ANF. It is not known whether it is these K and D antigens or other determinants associated with the H-2 complex that may actually provide the immune stimulation for ANF induction. The particular mechanisms that may be operating to induce ANF cannot be determined at present. We are continuing with experiments to define what parameters influence the appearance of ANF in alloantisera.