Immunologically mediated regulation of lymphoproliferation requires a self-recognition mechanism. This was sought by measuring the ability of blood lymphocytes to recognize transformed, autologous lymphocytes. Human blood lymphocytes incubated with phytohemagglutinin (PHA) for 72 hr, followed by mitomycin C treatment, induced blast transformation of autologous lymphocytes from all 28 healthy adults tested. Blastogenesis was measured by reactor cell incorporation of 3H-thymidine and was greater at 72 than at 144 hr. The role of PHA itself was assessed in several ways. The supernatant of washed, PHA-transformed lymphocytes did not stimulate normal autologous lymphocytes. Lymphocytes incubated with PHA for 1 hr or 72 hr before mitomycin treatment bound equivalent amounts of 131I-PHA; cells treated for 1 hr did not transform and did not stimulate autologous lymphocytes. By contrast, cells incubated for 72 hr did transform and stimulate autologous lymphocytes. Lytic sonication of PHA-transformed lymphocytes abolished their stimulating capability. An identical result was observed in allogeneic mixed lymphocyte reactions after lytic sonication of the stimulating cells. PHA itself maintained its stimulatory capability after sonication. Although N-acetyl-d-galactosamine (NAGAL) competes with PHA for lymphocyte membrane sites, incubation of reactor lymphocytes with NAGAL did not diminish their response to PHA-transformed autologous lymphocytes. These results strongly suggest the presence of autorecognition determinants on membranes of transformed lymphocytes. The relatively rapid reaction to these determinants is consistent with prior in vivo exposure.

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