Acute, Subchronic, and Chronic Exposure to a Simulated Urban Profile of Ozone: Effects on Extrapulmonary Natural Killer Cell Activity and Lymphocyte Mitogenic Responses

Abstract

Rats were exposed for 7, 3, 73, 52, or 78 wk to air or a simulated urban profile of O₃ designed to mimic diurnal exposure patterns frequently seen in worst-case summer environments. Daily exposures consisted of a background level of 0.06 ppm for a period of 73 h, a broad exposure spike rising from 0.06 to 0.25 ppm and returning to 0.06 ppm over 9 h, and a 2 h downtime. Integration of the spike portion of the exposure pattern was equivalent to a 9-h square-wave exposure pattern of 0.79 ppm. Rats were exposed to this profile 5 days/wk; weekend exposures were to background levels only Spleens were removed and blood was drawn at the end of the exposure periods. Spleen cells were assessed for natural killer cell (NKC) activity and responses to T-cell mitogens, phytohemagglutinin and concanavalin A, and the B-cell mitogen, Salmonella typhimurium glycoprotein. Peripheral blood leukocytes (PSU were also assessed for responses to T-cell mitogens. Sections from spleen, femur (including bone marrow), thymus, and mandibular, peribronchial, and mediastinal lymph nodes were taken from similarly treated rats and examined histopathologically O₃ exposure had no effect on NKC activity, nor were any O₃-related changes in mitogen responses or histopathology noted. Mitogen responses, but not NKC activity, were significantly depressed, presumably as a result of age, following the 52– and 78-wk exposures. PBL responses to mitogens were also lower following the 13-wk compared to 7– and 3-wk exposures. Effects of a single 3-h exposure to 7 ppm O, on spleen-cell responses to the same mitogens were also determined 0, 24, 48, and 72 h after exposure; there were also no effects due to this acute exposure.