Tissue distribution of restricted leukocyte common antigens. A comprehensive study with protein- and carbohydrate-specific CD45R antibodies.

A panel of monoclonal antibodies, specific for either protein or carbohydrate components of the leukocyte common antigen (LCA), were used to characterize the expression pattern of different variants of this antigen complex. Immunohistochemical and flow cytometric analysis was carried out on human lymphoid tissues from different anatomical compartments. We found that variations in terminal sialic acid or O-linked sugar moieties were associated with drastic differences in reactivity with some of the CD45R antibodies. For example, the carbohydrate determinants recognized by MT2 (CD45RA) and 2B11 (CD45) were not or were very weakly expressed on germinal center cells, whereas the carbohydrate determinant recognized by MT3 (CD45RB) was not expressed on the majority of mantle zone B cells. On the other hand, KiB3 (CD45RA) reacted with a protein determinant that is normally only exposed on mantle zone B cells but can be uncovered on marginal zone B cells and the CD45RA-positive T-cell subpopulation by enzymatic treatment. The findings suggest that differential biosynthesis and expression of the carbohydrate components of LCA are important mechanisms to generate additional LCA heterogeneity. Similar to the differential usage of the variable region, the exact carbohydrate composition is also linked to the stage of cell development. Heterogeneity in carbohydrate composition of the extracellular domain of LCA appears to enable interactions with different ligands, thereby holding the key to the regulation of LCA cytoplasmic tyrosine phosphatase activity.