Submitted on July 24, 2007
Accepted on October 31, 2007
Impact of ozone exposure on the phagocytic activity of human surfactant protein A (SP-A) and SP-A variants
Anatoly N. Mikerov1, Todd M. Umstead2, Xiaozhuang Gan1, Weixiong Huang1, Xiaoxuan Guo1, Guirong Wang1, David S. Phelps3, and Joanna Floros4*
1 Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States
2 Pediatrics, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States
3 Cellular and Molecular Physiology, Pediatrics, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States
4 Cellular and Molecular Physiology, Pediatrics, Obstetrics and Gynecology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States
* To whom correspondence should be addressed. E-mail: jfloros{at}psu.edu.
Surfactant protein A (SP-A) enhances phagocytosis of Pseudomonas aeruginosa (P. a.). SP-A1 and SP-A2 encode human (h) SP-A; SP-A2 products enhance phagocytosis more than SP-A1. Oxidation can affect SP-A function. We hypothesized that in vivo and in vitro ozone-induced oxidation of SP-A (as assessed by its carbonylation level) negatively affects its function in phagocytosis (as assessed by bacteria cell-association). To test this, we used P. a., rat alveolar macrophages (AMs), hSP-As with varying levels of in vivo (natural) oxidation, ozone-exposed SP-A2 (1A, 1A0) and SP-A1 (6A2, 6A4) variants. SP-A oxidation levels (carbonylation) were measured; AMs were incubated with P. a. in the presence of SP-A, and the phagocytic index was calculated. We found that: 1) the phagocytic activity of hSP-A is reduced with increasing levels of in vivo SP-A carbonylation; 2) in vitro ozone exposure of hSP-A decreases its function in a dose-dependent manner as well as its ability to enhance phagocytosis of either gram-negative or gram-positive bacteria; 3) the activity of both SP-A1 and SP-A2 decreases in response to in vitro ozone exposure of proteins, with SP-A2 being affected more than SP-A1. We conclude that both in vivo and in vitro oxidative modifications of SP-A by carbonylation reduce its ability to enhance phagocytosis of P. a. and that the activity of SP-A2 is affected more by in vitro ozone-induced oxidation. We speculate that functional differences between SP-A1 and SP-A2 exist in vivo, and that the redox status of the lung microenvironment differentially affects function of SP-A1 and SP-A2.
