Mouse mammary tumor virus production by thymic epithelial cells in vivo

Exogenous mouse mammary tumor viruses (MMTV) replicate in the mammary glands of infected females, and so infect the suckling pups. We have previously shown that the virus is rapidly disseminated to all the lymphoid organs, including the thymus. The present electron microscope immunohistochemical study describes the viral production site in the thymus. Viral buds and viral proteins were restricted to the thymus medullary epithelial cells. MMTV-encoded proteins were identified on the free viral particles and on the budding ones, the ribosomes, the membrane of the endoplasmic reticulum, and on the membrane of the medullary type II epithelial cell vacuolar network. The thymus medullary epithelial cells can thus integrate the virus and allow viral replication. The results support earlier results indicating that in some experimental conditions, epithelial cells may be involved in MMTV-induced negative selection by showing that thymic epithelial cells do express MMTV-encoded proteins.     

Role of epitope density in the induction of immunity and tolerance with thymus-independent antigens. I. Studies with 2,4-dinitrophenyl conjugates in vitro

The effect of different degrees of conjugation of levan, dextran, pneumococcal polysaccharide SIII and the copolymer of D-glutamic acid and D-lysine with the 2,4-dinitrophenyl determinant (DNP) on the immunogenic and tolerogenic capacity of its haptenic conjugates was investigated in vitro. A strikingly uniform effect of hapten conjugation was observed despite the marked difference in the mol. wt. and structure (branched or linear) of the carrier molecules. Regarding the anti-DNP response, low density conjugates were immunogenic but not tolerogenic (even at high doses), higher conjugates were both, depending on concentration, while very high density conjugates were only tolerogenic. These results confirm and extend earlier findings made with DNP conjugates of polymeric flagellin and indicate the probable generality of this principle. Together with parallel in vivo studies (Eur. J. Immunol. 1975. 5: 541), they reaffirm the importance of epitope density in the discrimination between immunity and tolerance.     

Role of epitope density in the induction of immunity and tolerance with thymus-independent antigens. IV. Selective tolerance and IgE response by DNP-levan conjugates.

Tolerance induction of IgE antibody-forming cells by dinitrophenylated levan (DNP-LE) conjugates was investigated in CBA mice. Antibody production was measured by passive coutaneous anaphylaxis on rat skin. Specific antibody neutralization was obtained with conjugates of different substitution degrees. Specific inhibition of IgE antibody production was obtained only with highly substituted conjugates. However, the epitope density required for inducing tolerance to antibody synthesis of the IgE class was lower than for other classes of immunoglobulins. The tolerance induced by DNP-LE was shown to affect only the anti-DNP B cells of IgE class without T cell participation. These results demonstrate that B cell precursors of all Ig classes are susceptible to tolerance induction and not to triggering by T-independent antigens.     

Role of epitope density in the induction of tolerance and immunity with thymus-independent antigens. III. Interaction of epitope density and receptor avidity.

The induction of B cell tolerance to 2,4-dinitrophenyl conjugates of polysaccharide antigens (levan or dextran) was studied in mice primed with keyhole limpet hemocyanin (KLH) or 2,4,6-trinitrophenylated KLH. The relationship of the epitope density of the tolerogen with avidity of B cell receptors (as judged indirectly by a plaque inhibition assay) was investigated. It was found that high avidity precursors (IgG) were tolerized by antigen of much lower epitope density, and at lower concentration, than were low avidity precursors (especially IgM cells). IgA cells were intermediate in behavior. These results suggest that the epitope density effect acts by ensuring a necessary degree and/or energy of antigen binding.     

Antigen-non-specific T-cell factor in B-cell activation. Origin, biological properties and failure to show a relationship to H-2.

A population of T cells sensitive to ALS treatment release a non-specific factor (NSF) capable of replacing T cells in the response of nude spleen cells to erythrocyte antigens. This factor cannot be removed by immunoadsorbents with specificities directed towards products of the H2 complex, nor by lentil lectin, unlike certain specific T-cell factors. Furthermore, it functions across histocompatibility differences between mouse strains. It has been directly demonstrated that this factor can influence both proliferation and differentiation of B cells in response to a restricted group of T-dependent antigens, of which donkey and sheep erythrocytes are such special cases.     

Rat anti-T15 monoclonal antibodies with specificity for VH- and VH-VL epitopes

BALB/c mice immunized with phosphorylcholine (PC) produce antibodies which are predominantly of the T15 idiotype. Monoclonal anti-T15 antibodies have been generated in a number of laboratories by allogenic or syngenic immunization. Most of these mouse monoclonal antibodies react with idiotopes that are in or near the PC-binding site and require the presence of both T15 heavy and T15 light chain variable regions. By immunizing rats with T15 immunoglobulins, we have obtained monoclonal antibodies that recognize idiotopes that are not near the antigen-binding site. Four of these rat anti-T15 monoclonal antibodies react with free T15 heavy chains and with T15 heavy chains associated with irrelevant light chains while four other rat monoclonal antibodies require the presence of both T15 heavy and T15 light chains. This battery of rat anti-T15 monoclonal antibodies is useful in searching for heterogeneity within the T15 antibodies and in following the expression of the T15 heavy chain variable region in different strains of mice.     

Comparison of in vitro immunogenicity, tolerogenicity and mitogenicity of dinitrophenyl-levan conjugates with varying epitope density.

The mitogenicity, immunogenicity and tolerogenicity of various DNP-levan (DNP-LE) conjugates were compared using in vitro methods. Anti-DNP antibody synthesis induced by DNP-LE conjugates was related to the epitope density of DNP, BUT WAS NOT AFFECTED BY Macrophage dependent and was not influenced by the degree of hapten conjugation. These results imply that mitogenicity of an antigen is not necessarily related to the specific triggering of B cells.     

Induction of a cross-reactive idiotype dextran-positive antibody response in two IgH-Cb mouse strains treated with anti-J558 cross-reactive idiotype antibodies

The effect of IdX-specific rabbit and allogeneic antiidiotype antibodies (Ab2) was investigated in vivo in Igh-Cb mouse strains with respect to the induction of a cross-reactive idiotype (IdX)-positive anti-alpha (1-3) Dextran (Dex) response. These C.B20 and C57Bl/6 mice have an allotype-linked incapacity to respond with IdX-positive anti-alpha (1-3) Dex antibodies upon conventional immunization with Dex B1355. 7 d after the rabbit Ab2 injections, IdX-positive Ig (Ab3) and IdX-positive anti-alpha (1-3) Dex antibodies (Ab1') were detected in the sera of each tested mouse. The affinity-purified Ab1' were idiotypically indistinguishable from reference BALB/c IdX-positive myeloma proteins and BALB/c anti-alpha (1-3) Dex antibodies (Ab1) in a competitive inhibition radioimmunoassay, while Ab3 Ig appeared idiotypically deficient and did not bind to Dex. The response to the alpha (1-6) linkage of Dex was not affected in these mice. A large fraction of the Ab1' and Ab3 responses of both mouse strains were of the IgG1 class. The Ab1' antibodies differed from BALB/c Ab1 by lower relative binding to five of eight tested Dex, and by expressing the Igh4b allotype determinants on the IgG1 antibodies. This study identifies the products of a VHDex gene that appears to be under regulatory control in the Ighb mice. Its association with the b haplotype suggests that this gene may differ structurally from the BALB/c VHDex gene.