NATURAL-KILLER-CELL ACTIVITY IS REDUCED IN ASSOCIATION WITH ORAL-CONTRACEPTIVE USE

Oral contraceptive (OC) use has been associated with increased inciden ce of a number of infections, but the mechanisms behind these changes is unclear. The present study compared OC users and nonusers in natura l kilter (NK) cell activity, NK phenotype, and illness frequency. Subj ects were 55 female medical students (l9 OC users, 36 nonusers). Three blood samples were obtained, 1 mo apart. Natural cytotoxicity was tes ted with a Cr-51 assay. Self reports of illness symptoms during the pr evious week were collected at each blood sampling. NK phenotype number was assessed by flow cytometry, Oral contraceptive users had lower na tural cytotoxicity and increased frequency of sneezing, gastrointestin al distress, runny nose, sore throat, coughing, and total illness symp toms, relative to nonusers. No differences were found between OC users and nonusers in NK phenotype number. These findings support the hypot hesis that differences between users and nonusers in infection rates m ight be due to alterations in NK activity.