NEUTROPHIL ADHESION MOLECULE EXPRESSION IS COMPARABLE IN PERINATAL RABBITS AND HUMANS

Background: Human newborns, particularly those born before full term, are more susceptible to bacterial infections as a result of impaired h ost defense mechanisms. Compared with adults, circulating leukocytes f rom human newborns (preterm and full-term gestations) and newborn rabb its (full-term gestation) have low resting levels of CD62L (L-selectin ) and do not significantly increase surface expression of CD18 after i nflammatory stimulation. To determine the potential utility of preterm rabbits in investigations of perinatal human conditions, the authors compared the surface expression of the beta(2)-integrin CD18 and CD62L (L-selectin) on polymorphonuclear leukocytes (PMNs) from perinatal ra bbits and perinatal humans, both under resting conditions and after in vitro activation with inflammatory stimulants. Methods: After erythro cyte lysis of whole-blood samples, leukocytes from 7-day-old, full-ter m (31-day gestation), and preterm (24-day gestation) rabbits, as well as full-term (37-42 week gestation) and preterm (27-36 week gestation) human newborns were prepared and stimulated ia vitro at 37 degrees C with either C5a or phorbol myristate acetate. After fluorescence label ing of CD18 and CD62L with monoclonal antibodies, PMN adhesion molecul e expression was assessed by flow cytometry. Results: Constitutive CD1 8 expression was not significantly different between perinatal and adu lt humans hut was reduced in all perinatal rabbits compared with adult s. Inflammatory stimulation caused significant increases in CD18 expre ssion in adult human PMNs but not in full-term and preterm newborns. C hanges in CD18 expression in adult and preterm rabbits after stimulati on, although in the same direction as humans, were more variable. In b oth species, constitutive CD62L expression on PMNs from all perinates was significantly lower than in adults. However, CD62L was shed to sim ilar degrees after inflammatory stimulation in all groups. Conclusions : Preterm rabbits may provide a potentially useful experimental model to study PMN adhesion and host defense in the perinatal period, partic ularly preterm gestations. Specific advantages and limitations of rabb its in such studies are discussed.