Acute exposure to morphine suppresses cytotoxic T-lymphocyte activity

Chronic exposure (11 days) to morphine has previously been shown to suppress splenic and peritoneal cytotoxic T-lymphocyte activity through mu-opioid receptors. The present study was undertaken to assess the effects of varying the frequency of exposure to morphine on cytotoxic T-lymphocyte activity in C3H/HeN mice immunized with C57BL/6 splenocytes. Mice subchronically treated with morphine (50.0 mg/kg) showed no measurable suppression of splenic natural killer activity or splenic or peritoneal cytotoxic T-lymphocyte activity. However, mice treated acutely with 50.0 mg/kg of morphine exhibited a significant suppression of peritoneal but not splenic cytotoxic T-lymphocyte activity. Naltrexone pretreatment of mice receiving an acute dose of morphine blocked the suppression, implicating the involvement of opioid receptors. Using column depletion chromatography, peritoneal exudate cells mediating cytotoxic T-lymphocyte activity were both CD4(+)CD8(-) and CD4(-)CD8(+). Collectively, the results suggest that the duration of opioid (morphine) exposure differentially affects peritoneal cytotoxic T-lymphocyte activity. These results may have important implications regarding immunity to viral infections in individuals who abuse drugs such as heroin.