p215 and p24: two membrane-associated proteins expressed on cloned cytolytic T-cells but not on cloned helper T-cells.

Cloned lines of murine alloreactive cytolytic and helper T cells were derived from secondary mixed leukocyte cultures. Cells from three TC lines and four TH lines were internally labeled with 35S-methionine and then disrupted by hypotonic lysis. Low density (plasma membrane-enriched) and high density (endoplasmic reticulum-enriched) membrane fractions were isolated from each cloned cell line and analyzed by SDS-PAGE under reducing conditions. Two proteins were identified which were associated with membrane fractions from each of the TC lines but none of the TH lines. One of these, p215, migrated as a broad band with an apparent molecular weight of 200-220 kD. The other, p24, migrated as a sharp band or closely spaced doublet with an apparent molecular weight of 24 kD. Immunoprecipitation studies using monoclonal antibodies to T200, LFA-1, Thy 1, and Lyt 2 revealed that p215 was a variant of T200 found on TC lines but not on TH lines. Treatment of solubilized membrane proteins from TH lines with anti-T200 precipitated a 180-195 kD protein band seen on each of the TH lines but none of the TC. In contrast, p24 was not precipitated by any of these monoclonal antibodies. It appears that p24 represents a previously unidentified protein which is unique to TC and thus deserving of further study as to its functional significance.