The relevance for the immunological responsiveness of an animal of selective entry to and egress from the lymph of antigenically reactive cells

Abstract

Although various forms of antigenic challenge of an animal can be shown to modify the capacity of its circulating lymphocytes to respond to the same antigen after re-exposure, the underlying mechanisms have not been elucidated. Of two groups of experiments concerned with the induction of unresponsiveness in circulating lymphocytes, those instances in which unresponsiveness has been produced in the circulating lymphocyte population of rodents challenged with conventional antigens have been claimed to reflect the sequestration of specifically reactive cells in fixed lymphoid tissues. Two observations with which the explanation is incompatible are that unreactive populations can be reactivated readily following their removal from the antigenically challenged animal and that apparently unreactive cells can modify the reactivity of normal populations of lymphocytes when they are transferred together to irradiated hosts. It is not difficult to demonstrate that plasma from rats recently challenged with antigen contains humoral factors able to interfere non-specifically with the reactivity of normal lymphocytes, and the possibility that similar influences may contributed to lymphocyte unresponsiveness after antigenic challenge cannot be dismissed. A second group of experiments, which have been interpreted as an example of selective removal of specifically reactive cells from the circulation, concern the loss of reactivity by parental strain lymphocytes which have been passaged through F1 hybrid hosts. In this situation it can be shown that not only have specifically reactive cells accumulated in the spleen, but also that the retained cells have been subject to a reversible inactivation. Consequently it is probable that the unreactivity of the passaged parental strain lymphocytes in these experiments results from a mechanism quite different from that responsible for the unreactivity of circulating lymphocytes observed in animals challenged with conventional antigens.