The leukocyte adhesiveness/aggregation test as an inflammation-related, plasma-dependent agglutination phenomenon

The leukocyte adhesiveness/aggregation test (LAAT) is a non-specific marker of inflammation. In the present study, we examined the expression of the CD11b/CD18 as well as the CD62L antigens on the surface of peripheral blood leukocytes in 84 patients with various inflammatory conditions and 60 controls by using whole blood flow cytometry. We also conducted several in vitro experiments in order to explain the mechanism of the leukocyte adhesiveness/aggregation. A significant (r= -0.36, p<0.001) negative correlation was found between the expression of CD62L on the surface of peripheral blood polymorphonuclears and the state of LAA. There was no correlation between the availability of the CD11b/CD18 antigen and the adhesive state of these cells. In a series of in vitro experiments, we could show that it is possible to significantly reduce the number of aggregated leukocytes in the peripheral blood by using dilutions with buffer but not with plasma. There is no change in the degree of aggregation following incubation at low temperature in the presence of an aerobic metabolism blocker or following incubation with a divalent ion chelator. Additionally, white blood cells could be seen to adhere to protein-rich areas in the peripheral slides. We assume that the state of LAA in the peripheral blood as revealed by the LAA test is more a plasma factor-dependent agglutination than a firm aggregation phenomenon. Factors other than the leukocyte integrins or selectins should be sought as being responsible for this LAA phenomenon.