Chemotaxis of horse polymorphonuclear leukocytes to N-formyl-L-methionyl-L-leucyl-L-phenylalanine.

Horse polymorphonuclear leukocytes (PMN) isolated from horse blood by sedimentation and isotonic lysis and having about 25% accompanying lymphocytes were as effective at chemotaxis as nearly pure PMN isolated by density gradient techniques. N-Formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP), used as a representative of the formylmethionyl peptides (produced by prokaryocytic organisms), was effective as a chemoattractant only at the high concentration of 10(-4) M. When serum was preincubated with FMLP at concentrations as low as 10(-8) M, the serum attracted horse PMN. This activity was not generated when heat-inactivated (56 to 60 C for 30 minutes) serum was used. A combination of FMLP and zymosan was no more effective than zymosan alone in generating serum chemoattractants. The results of this study indicate that the FMLP is a weak chemoattractant for horse PMN, but that FMLP has the capability similar to that of zymosan to activate complement to produce PMN chemoattractants.