Cellular immunity in the mouse. V. Further studies on leukemia virus activation in allogeneic reactions of mice: stimulatory parameters

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.

The 5936 Ig-idiotype(s): genetic linkage to Ig-Ch Loci, T-cell dependence of synthesis and possible specificities

5936-idiotype(s) are defined by a rabbit antiserum which was obtained by immunizing a mouse-immunoglobulin(MIg)-tolerant rabbit 5936 with B6 anti-CBA Ig from a single B6 mouse. These idiotypes were found on IgG1 molecules in sera from B6 mice immunized with cells carrying the IAk alloantigen, and they were associated with B6 Ig allotypes (Igh-1b). The particular interest of this idiotypic system is that antiserum 5936 also detects idiotypes (Id) on B6-T cells immunized in vitro with IAk alloantigen, and such T-cell Id were found to be associated with Ig allotypes. We attempted to show that the 5936-Id on Ig molecules were linked to Igh-1b allotypes by backcross analysis. In addition, it was investigated whether the 5936-Id response was a T-cell dependent response, and, if so whether there was any restriction in this T-B cell collaboration. Finally, we continued our studies on the specificity of 5936-Id+ Ig molecules. The present experiments show that 5936-Id are linked to Igh-1b allotypes and that the quantity of 5936-Id produced appears to be regulated by Ir genes in the H-2 complex. The synthesis of 5936-Id is T-cell dependent, and only Igh-1b allotype compatible T cells would collaborate with 5936-Id+ B-cell precursors. 5936-Id+ Ig molecules appeared not to have specificity against eco- and xeno-tropic viruses. However, monoclonal antibodies produced from B6-T-cell-reconstituted B6 nude mice may carry 5936-Id and have specificity for B6-T-cell membrane molecules. The relevance of these findings to the question of whether or not T and B cells display identical idiotypes are discussed.

Generation of F1 hybrid cytotoxic T lymphocytes specific for self H-2

Cytotoxic T lymphocytes specific for self H-2 antigens are generated by murine F1 hybrid (H-2 heterozygous) spleen cells cultured with irradiated parental (H-2 homozygous) splenocytes. The effectors bind to heterozygous and homozygous cells bearing the appropriate H-2 alleles but only lyse homozygous targets. Autoreactivity for membrane-bound molecules of normal cells may be a mechanism for regulating cellular interactions.

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

The radioimmune precipitation (RIP) assay was used to examine the antibody titres against endogenous AKR murine leukaemia virus (MuLV) in a number of antisera to lymphocyte (Ly) alloantigens. The sera from normal donor and unimmunized recipient mice used in raising the alloantisera were also examined for anti-MuLV activity. It was found that all the antisera had high anti-MuLV titres and that in all but one case alloantigen immunization augmented the anti-viral titres. The degree of augmentation did not appear to be related to the anti-MuLV titre in the donor strain sera. Three I-region antisera were also examined for anti-MuLV antibodies and were found to have lower anti-viral titres than the Ly antisera even though immunization to I-region products greatly augmented the anti-viral titre. These results caution against the use of Ly antisera in characterizing the phenotype of lymphoid tumour cells without prior virus absorption.

Autoimmunity, oncornaviruses, and lymphomagenesis

The interactions between aberrant immune responses and C-type oncornaviruses in mice are complex. These viruses may be activated during certain immune responses, e.g., histocompatibility reactions, in the face of chronic immunosuppression. Oncornaviruses, themselves, may induce autoaggressive cell-mediated responses in certain lymphoid subpopulations, and these autoimmune reactions may be important in subsequent lymphomagenesis. Parallel events may occur in other animal models, e.g., the NZB mouse, and in certain human disorders, e.g., Sjögren's syndrome, systemic lupus erythematosus, and myasthenia gravis.

Replication and persistence of measles virus in defined subpopulations of human leukocytes

Replication of Edmonston strain measles virus was studied in several human lymphoblast lines, as well as in defined subpopulations of circulating human leukocytes. It was found that measles virus can productively infect T cells, B cells, and monocytes from human blood. These conclusions were derived from infectious center studies on segregated cell populations, as well as from ultrastructural analyses on cells labeled with specific markers. In contrast, mature polymorphonuclear cells failed to synthesize measles virus nucleocapsids even after infection at a relatively high multiplicity of infection. Measles virus replicated more efficiently in lymphocytes stimulated with mitogens than in unstimulated cells. However, both phytohemagglutinin and pokeweed mitogen had a negligible stimulatory effect on viral synthesis in purified populations of monocytes. In all instances the efficiency of measles virus replication by monocytes was appreciably less than that of mitogenically stimulated lymphocytes or of continuously culture lymphoblasts. Under standard conditions of infection, all of the surveyed lymphoblast lines produced equivalent amounts of measles virus regardless of the major histocompatibility (HL-A) haplotype. Hence, no evidence was found that the HL-A3,7 haplotype conferred either an advantage or disadvantage with respect to measles virus synthesis in an immunologically neutral environment. A persistent infection with measles virus could be established in both T and B lymphoblasts. The release of infectious virus from such persistently infected cells was stable over a period of several weeks and was approximately 100-fold less than peak viral titers obtained in each respective line after acute infection.

Enhancement of mouse cytomegalovirus infection during host-versus-graft reaction

C3H/He mice chronically infected with murine cytomegalovirus were given skin allografts from histoincompatible BALB/c donors. A significant increase in cytomegalovirus titers occurred within 3 days after placement of the graft in the spleens and kidneys of the allograft recipients as compared with control animals. No significant changes in virus titers were detected in the salivary gland, lung, liver, or blood of allograft recipients. These results indicate that the host-versus-graft reaction alone can enhance murine cytomegalovirus in a chronically infected host and may help explain the high incidence of cytomegalovirus infection seen after renal and other allograft transplantation in man.

Activation of C-type viruses during skin graft rejection in the mouse. Interrelationships between immunostimulation and immunosuppression

Both mouse-tropic and zenotropic C-type RNA viruses were activated in BALB/c mice during rejection reactions against skin grafts from mice differing at the major histocompatibility locus (A/J) or sharing this locus (DBA/2). Animals that maintained their skin grafts following immunosuppression with antilymphocyte serum (ALS) or cyclophosphamide had a much higher incidence of virus-positivity than animals that did not receive ALS or cyclophosphamide, or that rejected their skin grafts despite immunosuppressive therapy. ALS itself activated type-C viruses from a small proportion of BALB/c mice whereas cyclophoshamide alone did not. Type C viruses were detected in spleens and regional nodes draining skin-graft sites between 1 and 2 weeks following transplantation; thereafter they reached maximum titers in spleens. Viruses were not detected at skin-graft sites, in tails or in thymuses of grafted animals. Virus activation was associated with splenic histological changes consisting of germinal center formation, diffuse hyperplasia of reticulum cells, depletion of periarteriolar lymphocytes and hyperplasia of red pulp hematopoietic elements.