CONTROL OF LEUKOCYTE FUNCTION-ASSOCIATED ANTIGEN-1-DEPENDENT CELLULARCONJUGATION BY DIVALENT-CATIONS

The control of integrin activation is fundamental to an understanding of the integrin-dependent cellular adhesion thought to be important fo r a plethora of basic cellular functions. Using a cell-cell conjugatio n assay the role of divalent cations in leucocyte function-associated antigen-1 (LFA-1)-dependent cellular adhesion was further investigated . The conjugation of interleukin-2 (IL-2)-activated lymphocytes to tum our cells was found to be energy dependent and required the presence o f various divalent cations, removal of which decreased the level of co njugation. Increased concentrations of calcium, magnesium and manganes e ions resulted in a corresponding increase in levels of conjugation. This increase in conjugation was LFA-1 dependent. Interestingly, when calcium ions were first removed from LFA-1, treatment of lymphocytes w ith magnesium and manganese ions gave significantly higher levels of c onjugation than in the presence of calcium. Using a simple displacemen t study, calcium ions were shown to displace magnesium ions resulting in decreased conjugation. However, calcium ions were unable to displac e manganese ions for binding to LFA-1. That manganese was exerting its effect via an LFA-l-dependent mechanism was confirmed using monoclona l antibodies to CD11a which negated the increased conjugation frequenc y due to manganese.