Surfactant proteins A and D in premature baboons with chronic lung injury (Bronchopulmonary dysplasia) - Evidence for an inhibition of secretion

Surfactant proteins A and D (SP-A and SP-D) are believed to participate in the pulmonary host defense and the response to lung injury. In order to und erstand the effects of prematurity and lung injury on these proteins, we me asured the amounts of SP-A and SP-D and their mRNAs in three groups of anim als: (?) nonventilated premature baboon fetuses; (2) neonatal baboons deliv ered prematurely at 140 d gestation age (ga) and ventilated with PRN O-2; ( 3) animals of the same age ventilated with 100% O-2, to induce chronic lung injury. In nonventilated fetuses, tissue and lavage SP-A were barely detec table in baboons of 125 and 140 d ga, but they equaled or exceeded adult SP -A concentrations (g/g lung dry wt) at 175 d (term gestation, 185 d). In co ntrast, SP-D was readily detectable in tissue and lavage at 125 and 140 d g a. When the baboons of 140 d ga were ventilated for 10 d with 100% oxygen t o produce chronic lung injury, the tissue concentration of SP-A was five ti mes greater than that of normal adults; 5P-D 16-times greater. Despite the sizable tissue pools of SP-A and SP-D, however, lavage SP-A was only 7% of that of normal adults and lavage SP-D just equaled the amount in normal adu lts. Nevertheless, because SP-D is normally in much lower concentration tha n is SP-A, their total comprised less than 12% of the SP-A and SP-D found i n the lavage of a healthy adult. The results indicate that in chronic lung injury, SP-A is significantly reduced in the alveolar space. SP-D concentra tion in lavage is about equal to that in normal adults, possibly because of the 16-fold excess in tissue, but the total collectin pool in lavage is st ill significantly reduced. Because these collectins may bind and opsonize b acteria and viruses, decrements in their amounts may present additional ris k to those premature infants who require prolonged periods of ventilatory s upport.