Membrane dynamics of lymphocyte interaction with antigen and tolerogen

Direct tolerance induction in mature B lymphocytes may resemble clonal anergy phenomenon

Several mechanisms have been postulated for direct induction of B-cell tolerance in mature B cells, such as the Bretscher and Cohn [5] hypothesis which states that an antigenic signal to B cells without the 'second signal' provided by T cells or lymphokines produces unresponsiveness. A second explanation is that tolerogens which cross-link immunoglobulin and Fc receptors abort the biochemical activation of the B cell via the phosphatidyl inositol pathway. Results of our studies are not consistent with either of these hypotheses. We speculated that DNP-MGG induces immunoglobulin receptor capping and internalization in mature B cells, but a suppressive signal is given to the B cell when DNP-MGG is present at the time of antigen receptor reexpression in a fashion similar to clonal anergy. The studies reported here test this hypothesis as a possible additional mechanism of direct B-cell tolerance. When pure DNP-specific B cells were incubated for 6 h with DNP-MGG in the presence of lymphokine-rich EL-4 supernatant, an immune response was induced; but 48 h preincubation with DNP-MGG in the presence of lymphokines induced tolerance. If B-cell cultures were preincubated with DNP-MGG for 6 h followed by a 24-hour incubation without conjugate and DNP-MGG was then added for the third preincubation period of 18 h (at a time when receptors are being reexpressed), tolerance was induced. Substitution of DNP-Ficoll antigen for DNP-MGG in either the first or third time period did not result in tolerance induction but substituting DNP-KLH during either of these two periods did result in tolerance.

The effect of cyclic nucleotides on tolerance induction by dinitrophenyl-isologous immunoglobulin G

When tolerance to a hapten is induced by injecting the hapten conjugated to isologous immunoglobulin (Ig) G (dinitrophenyl (DNP)-IgG), the hapten remains on the surface of the antigen binding cell (ABC) for the duration of the tolerant state. Although this has been interpreted as a receptor blockade of ABC, it does not necessarily indicate that physical blocking of antigen receptors is the only mechanism of tolerance. Data are presented which suggest that cyclic nucleotides play a role in the in vitro induction of tolerance by DNP-IgG. Agents that elevate intracellular cyclic adenosine 3',5' monophosphate (cAMP) levels were added to lymphocytes during tolerance induction in vitro by DNP-IgG. Dibutyryl cAMP, theophylline, aminophylline, and isobutyl alpha-methylxanthine were able to inhibit the induction of tolerance to DNP. On the other hand, addition of dibutyryl cyclic guanosine 3',5'-monophosphate (cGMP) to lymphocytes incubated with doses of DNP-IgG that ordinarily are too low to induce tolerance facilitated tolerance induction. The possible role of these intracellular second messengers in the induction to tolerance is discussed.