The responsiveness of efferent lymph cells to phytohaemagglutinin during the response of the popliteal node to dinitrophenylated bovine serum albumin.

Cells, recovered from the efferent lymphatics of the popliteal nodes of sheep during in vivo responses to dinitrophenylated bovine serum albumin (DNP-BSA), were examined for their responsiveness to phytohaemagglutinin (PHA) in vitro during the first 4--5 days of the immune response. The response was almost totally depressed when cells collected throughout the response were cultured with supra-optimal doses of the mitogen. Optimal and suboptimal doses of PHA resulted in greatly enhanced responses in cells collected in the first two periods (0--6 h; 6--12h) of the response; the presence of high doses of DNP-BSA in the culture media prevented the enhancement in the second period but had no adverse effects on the cells collected during the first 6 h. Efferent cells collected after 12 h generally showed decreased responses, this depression being maximal in cells collected 2--3 days after antigenic stimulation. Later in the response the cells again exhibited enhanced responses. The possible interpretations of these results in terms of regulation of the response are discussed.