Year of Publication
Robert P. Rapp
Pneumocystis carinii is an opportunistic fungal pathogen that causes lifethreatening pneumonia in immunocompromised individuals. Infants appear to be particularly susceptible to Pneumocystis (PC) pulmonary infections. The higher incidence of PC as well as other pulmonary infections among infants is likely due to an immature immune system. The neonatal lung environment is deficient immunologically in preterm as well as term infants (1, 2). Decreased phagocytic capacity of macrophages in newborns may increase the risk of infection from inhaled pathogens (1, 2). We have previously demonstrated that there is approximately a 3-week delay in the clearance of PC organisms from pup mouse lungs compared to adults. Herein, we demonstrate that there is also a 1-week delay in the infiltration of AMs in pup compared to adult PC-infected mice. We go on to show that there is a delay in pup versus adult lung macrophage phenotypic expression and cytokine production in response to PC organisms. We demonstrated that pup AMs are competent to produce cytokine in response to LPS and that stimulation with zymosan generates cytokine production in pup AMs that is comparable to adult cytokine production. These data indicate that pup lung macrophages are specifically poorly responsive to PC organisms and likely require exogenous stimulation to mount a significant immune response and expedite clearance of the organism. We go on to show that heat-killed Escheriae coli improves cytokine response, cellular infiltration and reduces organism burden in PC-infected pup mice. The clinically relevant cytokine, GM-CSF, has been used to improve the clearance of several pulmonary infections, including PC in adult animal models. We show that monotherapy with GM-CSF is insufficient to improve PC clearance in pup mice; however, when combined with TMP/SMX it improves PC clearance and maintains a reduced PC burden following discontinuation of therapy. Furthermore, we have shown that GM-CSF improves the ability of human infant lung macrophages to phagocytose PC organsms without generating an increased inflammatory response. These data suggest that combination therapy with TMP/SMX and GM-CSF may be a viable treatment option for infants failing or intolerant to standard therapy.
Empey, Kerry McGarr, "NEONATAL IMMUNE MODULATION TO IMPROVE PNEUMOCYSTIS CLEARANCE" (2007). University of Kentucky Doctoral Dissertations. 500.