Interactions between lymphocyte membrane molecules. I. Interaction between B lymphocyte surface IgM and Fc IgG receptors requires ligand occupancy of both receptors.

The independent B lymphocyte surface membrane receptors IgM and Fc IgG receptors were evaluated for interactions using immunoflourescence. Ligand [F(ab')2 anti-mu]-induced capping of surface IgM resulted in capping of Fc IgG receptors only if the latter were occupied during the capping process by: (a) soluble antigen-antibody complexes that themselves provided insufficient cross-linking to result in capping; or (b) monomeric IgG at physiologic concentrations (or less) either purified or as normal serum. Ligand-induced capping of Fc IgG receptors did not result in capping of surface IgM occupied by monomeric F(ab') anti-mu. Control experiments showed that ligand binding to or capping of only one of these two receptors has no effect on the other, and that there were no cross-reactions. The interaction appears specific in that ligand-induced capping of surface IgM did not induce capping of ligand-occupied surface IgD or I-A antigens. Thus, there appears to be a specific interaction between ligand-bound surface IgM and ligand-bound Fc IgG receptors on the B lymphocyte surface. The results also indicate that binding of monomeric IgG produces a reversible alteration in the Fc IgG receptor leading to association with ligand-bound surface IgM. Because Fc IgG receptors are continuously exposed to monomeric IgG in vivo, these results suggest that whenever surface IgM is involved in a B lymphocyte response to an immunologic stimulus, the Fc IgG receptor is also involved.

Detection of non-H2 antigen(s) which, like Ia antigens, are associated with the Fc receptor of B lymphocytes.

Antibodies contained in an A/J anti-B10 antiserum, when tested on lymphocytes from B10.A mice, were shown to bind to both B and T cells and to inhibit the binding of Ig complexes to the Fc receptors of B lymphocytes. These antibodies could be removed by absorption with B10.D2 lymphocytes. Similar results were obtained with lymphocytes from two to six (B6A)F1 x A/J backcross mice which had H-2a/a genotype. These data indicate that alloantigens determined by at least one non-H-2 locus are associated with or a part of Fc receptors. These antigens may be similar in structure and function to Ia antigens.

Simian tumor virus isolate: demonstration of cytopathic effects in vitro.

Several cell lines that were derived from primates and inoculated with virus originally obtained from a spontaneous mammary carcinoma showed cytopathic effects characterized by multinucleation. These cytopathic effects appeared as early as 24 holurs after inoculation. Multinucleated cells contained virus particles characteristic of the original virus isolate.

Responses of infant rhesus monkeys to inoculation with Mason-Pfizer monkey virus materials.

Rhesus monkeys neonatally inoculated with Mason-Pfizer monkey virus (M-PMV) and virus-infected cells frequently developed viral and/or bacterial pneumonia and enteritis. Three characteristic hematologic patterns occurred among the inoculated animals and correlated well with the probability of survival. Postmortem examination of the animals revealed lymphadenopathy and thymic atrophy. M-PMV was present in lymph nodes, blood, brain, spleen, thymus, kidneys, and bone marrow. The disease induced in some animals had characteristics suggestive of a slow-virus-induced autoimmune response.

Effects of various forms of monoclonal anti-Fc gamma R II (2.4G2) on B lymphocyte responses.

The effects of monoclonal anti-Fc gamma R II (2.4G2) in various forms on B lymphocyte proliferation and antibody (mu) secretion in vitro were evaluated. Soluble native 2.4G2 did not stimulate or inhibit the responses of B lymphocytes, either unstimulated or stimulated with rabbit F(ab')2 anti-mouse mu (anti-mu) plus lymphokines (the supernatant of Concanavalin A stimulated rat spleen cells). The failure of native 2.4G2 to affect responses was observed over a broad range of concentrations, and even when the B lymphocytes were incubated with the 2.4G2 for 24 hr prior to stimulation with anti-mu and lymphokines. Similarly, soluble chemically cross-linked 2.4G2 failed to affect B lymphocyte responses. Binding studies indicated that this failure was not due to a lack of binding and suggested that the polymerized 2.4G2 was cross-linking at least four Fc gamma R II. Larger multimers of 2.4G2 could not be evaluated due to a loss of binding activity. In contrast to the above results, 2.4G2 which was capable of extensively cross-linking Fc gamma R II (2.4G2 bound to Sepharose) or of cross-linking Fc gamma R II to surface IgM (2.4G2 hetero-cross-linked with anti-mu) specifically inhibited B lymphocyte responses to anti-mu and lymphokines. Antibody secretion was affected more than proliferation. These results provide additional evidence that Fc gamma R II regulate the responses of B lymphocytes, and suggest that cross-linking of more than four Fc gamma R II is necessary to generate the inhibitory signal. Further, the results indicate that the ligand does not have to be internalized in order to generate the regulatory signal. Finally, the results with the heterodimer suggest that it may be possible to regulate a particular antibody response using anti-Fc gamma R II cross-linked to antigen or to anti-receptor antibody (e.g. an anti-idiotype).

Interactions between lymphocyte membrane molecules. II. Characterization of an interaction between B lymphocyte surface IgD and Fc IgG receptors that differs from the surface IgM-Fc IgG receptor interaction.

The B lymphocyte surface membrane receptors IgD (sigD) and Fc IgG receptors (Fc gamma R) were evaluated for interactions by means of immunofluorescence. Ligand-(F(ab')2 anti-delta) induced capping of sIgD resulted in co-capping of Fc gamma R if the latter were occupied during the capping process by soluble antigen-antibody complexes (which themselves provided insufficient cross-linking to result in capping), but not if the Fc gamma R were occupied by monomeric IgG or unoccupied. Capping of Fc gamma R by highly cross-linked complexes did not cause co-capping of sIgD occupied by monomeric F(ab') anti-delta. The interaction between sIgD and Fc gamma R was specific in that cross-reactions between ligands were excluded and ligand-induced capping of sIgD did not cause co-capping of ligand-occupied sIgM or I-A antigens. The sIgD-Fc gamma R interaction occurred on only approximately 60% of B lymphocytes, and this B cell subpopulation did not correlate with other B cell subpopulations (CBA/N strain B cells and B cells bearing either large or small amounts of sIgD). The sIgD-Fc gamma R interaction differed from the sIgM-Fc gamma R interaction in that co-redistribution of the Fc gamma R was occupied by monomeric IgG and involved nearly all B lymphocytes. The qualitative and quantitative differences between the sIgD-Fc gamma R and sIgM-Fc gamma R interactions suggest a mechanism whereby the two antigen receptors could provide different signals to the B lymphocyte.

Virus susceptibility of a new simian cell line of fetal origin.

The cultivation and characterization of a cell line derived from the foreskin of a fetal, rhesus monkey (rhfs2) are described. This cell line has proven satisfactory for isolation and assay of a variety of viral agents of human and simian origin. Virus titrations performed on foreskin cells yielded titers comparable to, or higher than, those obtained in rhesus monkey kidney cells (LLC-MK2). Replicate isolation attempts in our laboratory from simian clinical specimens have proven rhfs2 superior to LLC-MK2 for ease of detection and frequency of isolation.