LFA-3 delta D2: a novel in vivo isoform of lymphocyte function-associated antigen 3.

Lymphocyte function-associated antigen 3 (LFA-3) has previously been described as occurring as two isomers in vivo, a transmembrane (TM) form and a glycosyl phosphatidylinositol (GPI)-linked form, differing only in their membrane anchoring mechanism. A third isoform, LFA-3 delta D2, which has the cytoplasmic tail of TM LFA-3 but a truncated extracellular domain, has been identified in vitro. We report that the LFA-3 delta D2 isoform, identified by RT-PCR analysis and DNA sequencing, is also present in vivo and appears to share a signal sequence with the TM and GPI isoforms. Expression of LFA-3 delta D2 was observed in both normal and diseased human buccal mucosa and gingiva. Thus, while specific functional differences between isoforms remain to be established, our results show that LFA-3 delta D2 is constitutively expressed in vivo, along with the other, previously described, isoforms of LFA-3.