Ontogeny of neutrophil chemotaxis in fetal lambs

Ontogeny of neutrophil chemotactic response using endotoxin activated adult sheep plasma as a source of complement derived chemotactic factor was examined in fetal lambs of gestational age 120-150 days. (Gestational period in sheep is approximately 150 days.) Neutrophils from fetal lambs of gestational age 120-130 days failed to respond to this chemotactic factor whereas neutrophils from fetal lambs above 131 days of gestational age responded at levels comparable to adult values. Examination of neutrophil chemotaxis in older fetuses using a different chemotactic factor derived from mitogen stimulated adult mononuclear cells revealed a selective failure of fetal neutrophils to respond to lymphocyte-derived chemotactic factor in the presence of a normal response to complement derived chemotactic factor. Among prematurely delivered twin fetuses alterations in comparison with the first twin or age-matched controls in peripheral neutrophil count (increase) and in chemotaxis (increase or decrease) were noted in second of twins delivered greater than or equal to 20 min after the first lamb, suggesting an extreme sensitivity of neutrophil functions to a variety of influences, similar to that seen in humans.