Neutrophil and monocyte phagocytosis in depressed patients.

1. Monocyte and neutrophil phagocytosis was investigated in a group of depressed patients during the active phase of their illness and following recovery. The results were compared with those obtained from a group of schizophrenia and manic patients and with age and sex matched controls. Neutrophil phagocytosis was reduced in all three patient groups during the active phase of the illness but returned to control values on recovery. Monocyte phagocytosis was however increased but while it returned to control values following recovery of the depressed patients, it remained raised in the manic and schizophrenic patients. 2. T-cell replication in response to a mitogen challenge was also investigated in the depressed patients. This was found to be significantly reduced in the depressed patients during the active phase of the illness and remained reduced following their recovery. 3. The results suggest that the changes in phagocytosis and T-cell replication are state and trait markers respectively of depression. 4. A differential white blood cell count revealed that the neutrophil number was increased and the monocytes decreased, in the depressed patients during the active phase of the illness, but returned to normal values on recovery. 5. The factor(s) responsible for the changes in these various aspects of the immune function is unknown. However, evidence is presented that the changes are not due to hypercortisolaemia or to the direct effects of the psychotropic medication on phagocytosis or T-cell replication.