Functionally defined CD164 epitopes are expressed on CD34(+) cells throughout ontogeny but display distinct distribution patterns in adult hematopoietic and nonhematopoietic tissues

Three distinct classes of epitopes on human CD164 have been identified. Two of these, recognized by the monoclonal antibodies 105A5 and 103B2/9E10, ar e the CD164 class I and class II functionally defined epitopes, which coope rate to regulate adhesion and proliferation of CD34(+) cell subsets. In thi s article, we demonstrate that these 2 CD164 epitopes are expressed on CD34 (+) cells throughout ontogeny, in particular on CD34(+) cell clusters assoc iated with the ventral floor of the dorsal aorta in the developing embryo a nd on CD34(+) hematopoietic precursor cells in fetal liver, cord blood, and adult bone marrow. While higher levels of expression of these CD164 epitop es occur on the more primitive AC133(hi)CD34(hi)CD38(1o/-) cell population, they also occur on most cord blood Lin(-)CD34(lo/-)CD38(lo/-) cells, which are potential precursors if or the AC133(hi)CD34(hi)CD38(lo/-) subset. In direct contrast to these common patterns of expression on hematopoietic pre cursor cells, notable differences in expression of the CD164 epitopes were observed in postnatal lymphoid and nonhematopoietic tissues, with the class I and class II CD164 epitopes generally exhibiting differential and often reciprocal cellular distribution patterns. This is particularly striking in the colon, where infiltrating lymphoid cells are CD164 class I-positive bu t class Ii-negative, while epithelia are weakly CD164 class Ii-positive. Si milarly, in certain lymphoid tissues, high endothelial venules and basal an d subcapsular epithelia are CD164 class Ii-positive, while lymphoid cells a re CD164 class I-positive. It therefore seems highly likely that these CD16 4 class I and II epitopes will mediate reciprocal homing functions in these tissue types. (C) 2000 by The American Society of Hematology.