Immunopotentiation with BCG. II. Modulation of the Response to Sheep Red Blood Cells2

Abstract

The immunologic response to sheep red blood cells (SRBC) was used to study the immunopotentlating action of BCG. The wave of cell proliferation, which preceded by 24 hours the production of direct plaque-forming cells (PFC) in the popliteal lymph node, was amplified about threefold in nodes primed by a previous footpad inoculation of living BCG; the total numbers of direct and indirect PFC in the node at peak production were increased approximately 15-fold. The response to SRBC was associated with a delayed type of hypersensitivity (DTH) mediated by θ-bearing cells. In unprimed animals, DTH (measured as increased footpad thickness) was maximal in 6 days, but reached a much higher maximum (threefold) within 4 days in animals primed with BCG. Potentiation occurred only when BCG and SRBC reached the same regional node. Cell proliferation in responding nodes correlated closely with resulting levels of DTH. As cell proliferation in response to BCG increased, cell response increased proportionally to super-added stimulation by SRBC. Maximum potentiation was achieved when SRBC were introduced on day 14 of the response to BCG.