COGNATE INTERACTION BETWEEN HUMAN-LYMPHOCYTES AND EOSINOPHILS IS MEDIATED BY BETA-2-INTEGRINS AND VERY LATE ANTIGEN-4

Here the cognate interactions between human eosinophils and lymphocyte s are studied. These interactions were measured in a double-colored FA CS analysis by applying fluorescent red eosinophils (stained with hydr oethidine, 40 mu mol/L) and fluorescent green lymphocytes (stained wit h sulfidofluorescein diacetate, 100 mu mol/L) in a ratio of 1:3, When normal eosinophils were mixed with a total lymphocyte preparation in s tirred suspensions (37 degrees C), no physical interaction was present between both cell types. However, the addition of phytohemagglutinin and PMA resulted in a clear aggregation response between both cell typ es (up to 30% of the eosinophils interacted with lymphocytes after 15 minutes), CD8(+)- and CD4(+)-positive T cells contributed equally to t he heterotypic aggregation response. It is interesting that when lymph ocytes were pretreated with phytohemagglutinin or eosinophils with pho rbol myristate acetate and subsequently washed, the cells still intera cted with unstimulated counterparts. The heterotypic interaction betwe en lymphocytes and eosinophils is blocked by monoclonal antibodies dir ected against the beta-chain of the beta(2)-integrins (CLB LFA1/1; CD1 8) and the alpha-chain of very late antigen-4 (VLA-4) (HP2/1; CD49d), indicating that both the beta(2)-integrins and VLA-4 contributed to th is heterotypic interaction. When eosinophils bound to PHA-treated lymp hocytes, the cells exhibited an activated phenotype that was character ized by an enhanced expression of CD66b and CD11b, The cells interacte d with each other provided that an intact cellular metabolism was pres ent-that is, no interaction was seen after treatment with the glycolys is inhibitor sodium mono-iodoacetate, In conclusion, our findings indi cate that eosinophils can physically interact with lymphocytes provide d that the beta(2)-integrins and/or VLA-4 are in an activated state.