Two novel T cell specific activation
antigens were characterized and were defined by
monoclonal antibodies developed against
mitogen-stimulated human T cells. These
antigens, designated as
L-35 and L-36 were expressed on both the CD 4(Leu-3) and the CD 8(Leu-2) subsets of activated but not resting T cells. Moreover these
antigens were not expressed on a number of T, B, and myeloid tumor cell lines.
L-35 and L-36 were expressed on
interleukin 2 (IL 2)-dependent cloned T cell lines, and were weakly expressed on the T cell
tumor line, HSB-2.
L-35 was expressed on granulocytes and a small subset of thymocytes. SDS-PAGE analysis of 125I-labeled lysates from
phytohemagglutinin (PHA)-activated T cells demonstrated that
L-35 existed as a complex of 32,000 and 97,000 dalton
polypeptides under reducing and nonreducing conditions. Anti-L-36 immunoprecipitated a 90,000 dalton structure from PHA-activated cell lysates prepared with
CHAPS detergent. When immunoprecipitates were analyzed from [35S]
methionine labeled lysates, anti-L-35 precipitated only the 97,000 dalton component, suggesting that the 32,000 dalton subunit of
L-35 complex was not synthesized by the activated cell population. Furthermore anti-L-35 did not immunoprecipitate a 32,000 dalton component from 125I-labeled lysates of anti-Leu-4 or Con A-activated cells, suggesting that the 32,000 dalton component of the
L-35 complex may represent a subunit of PHA. The 32,000 dalton
protein could not, however, be precipitated from cells incubated with PHA for less than 1 day. These results suggested that anti-L-35 recognizes a 97,000 dalton structure expressed on activated T cells, and that upon activation by PHA, becomes associated with a subunit of this
mitogen.