EVIDENCE FOR ANTIGEN RECOGNITION BY NONSPECIFIC CYTOTOXIC-CELLS - INITIATION OF H-3-THYMIDINE UPTAKE FOLLOWING STIMULATION BY A PROTOZOAN PARASITE AND HOMOLOGOUS COGNATE SYNTHETIC PEPTIDE

Catfish nonspecific cytotoxic cells bind to and lyse certain protozoan parasites and tumor cells. Target cell binding is facilitated by reco gnition of (minimally) one antigenic determinant. Binding to this dete rminant initiates multiple signalling pathways in NCC including protoo ncogene kinase phosphorylation, regulation of phosphatase activity and increased membrane receptor expression. In the present study, highly purified NCC were activated in vitro with the protozoan parasite Tetra hymena pyriformis, with a multiple antigenic peptide (MAP) composed of the cognate antigenic determinant of this parasite (i.e. natural kill er target antigen/NKTag) and NCC were activated with a monoclonal anti body specific for the NCC receptor which binds NKTag. NCC were purifie d by Percoll density gradients and negative selection by panning (2x) over anti-sIg specific mab 9E1. In 5 day proliferation experiments, tr eatment of NCC with immobilized Tetrahymena initiated a significant in crease in uptake of tritiated thymidine, This appeared to be a primary response in that NCC from in vivo parasite primed catfish did not hav e secondary-like proliferation responses. Stimulation of NCC with immo bilized synthetic peptides composed of the cognate antigenic determina nt of this parasite (i.e. MAP) also caused significant increased uptak e of tritiated thymidine. An indication that NCC recognize a specific antigenic determinant was that sMAP (i.e. peptides composed of the sam e amino acids as MAP but in a scrambled sequence) failed to increase i ncorporation. Similar to the MAP results, mab 5C6 binding to NCC also caused increased thymidine uptake. To determine if an IL-2 cosignal wa s required to achieve optimum activation responses by NCC, different c oncentrations of human recombinant IL-2 (rHuIL-2) were tested individu ally or as costimulants. Co-treatment of NCC with rHuIL-2 and any of t he three stimuli (parasite, MAP, mab 5C6) did not produce increased pr oliferation of NCC. These studies demonstrated that NCC specifically r ecognize an antigenic determinant on protozoan parasites and binding t o this antigen produces an activation signal that may have important c onsequences for elicitation of innate immunity. (C) 1998 Elsevier Scie nce Ltd. All rights reserved.