Ly-6I, a new member of the murine Ly-6 superfamily with a distinct patternof expression

A new member of the mouse Ly-6SF, designated Ly-6I, has been isolated as a gene homologous to a segment of the Ly-6C gene. A single allelic difference in the mature protein sequence was identified, which is similar to other L y-6SF members. Ly-6I mRNA has been detected in a wide range of tissues and cell lines, and a rabbit polyclonal Ab has been used to determine that Ly-6 I protein is present at a low constitutive level on cell lines from several different lineages. In contrast to Ly-6C and Ly-6A/E, the Ly-6I gene is on ly weakly responsive to IFNs, Expression in vivo is most abundant on bone m arrow populations and is coexpressed with Ly-6C on granulocytes and macroph ages. However, Ly-6I is also expressed on immature B cell populations that do not express Ly-6C, Expression on mature B cells in spleen is uniformly l ow. Similarly, Ly-61 is expressed on TCRlow/int, but not TCRhigh, thymocyte s. Ly-6I is re-expressed on Ly-6C(high) T cells in the periphery. Thus, Ly- 6I may be a useful marker to define maturation stages of both T and B lymph ocytes as well as subsets of monocytes and granulocytes.