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Comparative ultrastructure and expression of L-selectin on bovine alphabeta and gammadelta T cells
J G Leid1, C A Speer, M A Jutila
1Veterinary Molecular Biology, Montana State University, Bozeman 59717, USA.
Compared to most alphabeta T cells, bovine gammadelta T cells express two to five times the level of L-selectin and have a much higher capacity to roll on monolayers of endothelial cells, platelets, and leukocytes in assays done under physiological flow. To gain additional insight into the basis for these differences, scanning (SEM) and transmission (TEM) electron microscopy were used to compare the cellular ultrastructure of bovine gammadelta and alphabeta T cells and to study the expression of L-selectin on these cells. It is interesting that gammadelta T cells had more than twice as many microvilli and other surface projections on a per cell basis as alphabeta T cells. This was not due to the gammadelta T cell being larger; after adhesion and fixation procedures used for the EM studies, gammadelta T cells averaged 3.9 +/- 0.01 microm in diameter, whereas alphabeta T cells were slightly larger (5.7 +/- 0.01 microm in diameter). As previously shown for human neutrophils and lymphocytes, L-selectin was preferentially localized to the tips of the microvilli. In contrast, WC1, a lineage-specific antigen on gammadelta T cells, was localized on the plasmalemma between the microvilli. Our findings suggest that more effective rolling of gammadelta T cells in various in vitro flow assays may be due to the greater number of microvilli on gammadelta T cells leading to a higher number of contact sites during adhesion events. In addition, this physical parameter may explain the increased level of L-selectin expression on gammadelta versus alphabeta T cells because L-selectin is clustered at the tips of microvilli.
Compared to most alphabeta T cells, bovine gammadelta T cells express two to five times the level of L-selectin and have a much higher capacity to roll on monolayers of endothelial cells, platelets, and leukocytes in assays done under physiological flow. To gain additional insight into the basis for these differences, scanning (SEM) and transmission (TEM) electron microscopy were used to compare the cellular ultrastructure of bovine gammadelta and alphabeta T cells and to study the expression of L-selectin on these cells. It is interesting that gammadelta T cells had more than twice as many microvilli and other surface projections on a per cell basis as alphabeta T cells. This was not due to the gammadelta T cell being larger; after adhesion and fixation procedures used for the EM studies, gammadelta T cells averaged 3.9 +/- 0.01 microm in diameter, whereas alphabeta T cells were slightly larger (5.7 +/- 0.01 microm in diameter). As previously shown for human neutrophils and lymphocytes, L-selectin was preferentially localized to the tips of the microvilli. In contrast, WC1, a lineage-specific antigen on gammadelta T cells, was localized on the plasmalemma between the microvilli. Our findings suggest that more effective rolling of gammadelta T cells in various in vitro flow assays may be due to the greater number of microvilli on gammadelta T cells leading to a higher number of contact sites during adhesion events. In addition, this physical parameter may explain the increased level of L-selectin expression on gammadelta versus alphabeta T cells because L-selectin is clustered at the tips of microvilli.