Role of immune complexes in the humoral leukocyte adherence inhibition test

Summary The humoral leukocyte adherence inhibition (H-LAI) assay has recently been found to measure an antitumor immunefactor. In this assay, trypsinized leukocytes from control persons are used as indicator cells and 0,25% serum from the patient is added to the assay system together with the relevant tumor antigen.In the present work, evidence is presented that the H-LAI response is mediated through in vitro-formed immune complexes. Different antibody-antigen pairs (anti-albumin — albumin; anti-₂microglobulin — ₂microglobulin; anti-carcinoembryonic antigen — carcinoembryonic antigen; anti-transferrin — transferrin) have been added to the assay mixture. A significant H-LAI response was observed when immune complexes were formed. On the other hand, when unrelated antibody — antigen pairs were added, no response was found. The specificity was demonstrated in experiments where two different antibodies were added simultaneously and the response tested both against the two corresponding antigens and against unrelated antigens.Since the same trypsinized indicator cells can be used for different immune complexes, it is likely that the response is mediated through common receptors on the cell surface with affinity for immune complexes, i.e., Fc-receptors. Presumably, the H-LAI test gives response to immune complexes in general and is as such not specific. The specificity is achieved through the addition of specific antigen and the subsequent in vitro formation of immune complexes.