In vitro studies of natural killer cell activity in post traumatic stress disorder patients. Response to methionine-enkephalin challenge.

Attempts to define biological parameters that may be specifically associated with the pathophysiology of post traumatic stress disorder (PTSD) have met with only limited success, reflecting perhaps the practical limitations resulting from the high frequency of comorbidity of this condition with Axis I, II and III psychiatric diagnoses. We now report our studies on natural killer cell activity (NKCA), and the response of this cellular immune function to an in vitro methionine-enkephalin (MET) challenge in a population of Vietnam veterans with PTSD. Due to the characteristics of our PTSD patients, our protocol included four sex-matched, age-comparable control groups: (1) chronic alcoholics, (2) chronic drug abusers excluding alcohol, (3) chronic users of alcohol and other drugs of abuse and (4) drug-free, healthy volunteers. Although these groups did not significantly differ in their "baseline" NKCA, significant findings emerged from their response to preincubation with MET (10(-10), 10(-8) and 10(-6) M; 40:1 effector-to-target cell ratio). To minimize interindividual variations in the expression of NKCA each subject was used as its own control. Whereas peptide challenge resulted in an increase in NK lytic function in a subpopulation of group four (one or more MET concentrations, 8 out of 22 subjects), it produced mixed results in samples from individuals in group 2, and in general failed to elicit NKCA changes in the samples from participants in groups 1 and 3. Nine of the thirteen PTSD patients responded to MET preincubation with decreases in NKCA, which in five of them reached values below 20% of baseline for the three peptide concentrations tested. These findings may suggest that the "stress factor" in Vietnam veterans with PTSD plays a role in downmodulating NK lytic function in response to an in vitro MET challenge, an effect that appears to be potentiated by the use of drugs of abuse other than alcohol. The possible clinical relevance of these findings, including the identification of a subgroup of PTSD patients on the basis of immunological tests such as the one described in this work, deserves further investigation.