Induction of autoantibodies to red blood cells by polyclonal B-cell activators

THE ability to distinguish self from non-self is a fundamental property of the lymphoid system. One hypothesis for immunocyte triggering1 proposes that the encounter between antigen and immunoglobulin receptors results in irreversible tolerance, whereas activation requires additional signals, thus ensuring that tolerance to self-antigens will always be the first and easiest event to achieve. An alternative view is that the self-non-self discrimination is carried out by T cells2,3, whereas B cells could never be made tolerant to thymus-dependent antigens, including autologous antigens, because these antigens cannot deliver any signal to B cells by interacting with the Ig or any other B-cell receptor4,5. Experimental support for this notion has been obtained by the demonstration that tolerance to autologous antigens can be broken by the injection of cross-reacting antigens6 and that there are antigen-binding human B cells able to bind human thyroglobulin3. To distinguish between the two hypotheses, it is necessary to determine whether tolerance to self-antigens exists at the B-cell level. This can be done by treating lymphocytes with polyclonal B-cell activators (PBA) and studying antibody formation against autoantigens, for PBA are competent to active B cells of any specificity and thus to reveal the total V gene repertoire of the B cells. We have activated bovine spleen cells in culture with PBA (lipopolysaccharide (LPS) from Escherichia coli 055 : B5 and purified protein derivative (PPD) of tuberculin) and studied the number of plaque-forming cells (PFC) appearing against autologous red cells and heterologous red cells coated with the hapten NNP. In all experiments, the spleen cells and the red cells were derived from the same animal. We found that PBA-activated bovine lymphocytes synthesised autoantibodies agains their own red cells.