Characteristics of immunological memory in mice. II. Resistance of nonrecirculating memory cells to antigen-mediated suppression of the secondary antibody response.

Mice were primed and subsequently challenged at various times with subcutaneous injections of sheep erythrocytes, and some characteristics of the secondary responses in the draining brachial and axillary lymph nodes were investigated. It was found that the secondary response within primed nodes was resistant to immunological preemption, a competition-like phenomenon which severely depresses primary responses. Since it was also shown that circulating memory cells could be inhibited by preempting injections of antigen, it was concluded that the resistance of primed nodes to preemption was due to the presence within them of a nonrecirculating subpopulation of memory cells. The size of this population was dependent both on the amount of priming antigen and the time after priming. The observation that the response given by these cells remained unaffected by doses of antigen which could depress a primary response does not favor the view that suppression of immune responses by preemption or antigenic competition is due to a factor which acts directly and indiscriminately on all immunologically competent cells.