The X-Y-Z scheme of immunocyte maturation. V. Paralysis of memory cells.

A concentration of 5 mg/ml bovine serum albumin (BSA) prevents the in vitro elicitation of a secondary response in primed rabbit popliteal lymph nodes, if it is left in contact with the node fragments for the first 6 days of culture. No antibody formation can be detected at any time during the culture period in most cases, although occasional fragments are resistant to inhibition. Reducing the exposure time to the first 3 days of culture delays the peak of the antibody response. The inhibition is antigen specific. Reconstruction experiments demonstrate that the inhibition is not due to antigen masking of the antibody. Even shortly after optimal stimulation, the addition of 5 mg/ml BSA to the fragments was not able to prevent a normal antibody response. The implications of these findings are that (a) a high antigen concentration suspends the memory cell in a reversibly paralyzed state, (b) memory cells have a heterogeneous susceptibility to inhibition, (c) once induced, the antibody response cannot be inhibited by antigen overloading, (d) unresponsiveness in a primed animal can be due to either exhaustion of the memory cell population or paralysis of the memory cell.