Forced swimming test decreases chemotactic responsiveness and expression of CD11a in rat monocytes.

Objectives: Previous reports have shown that the depressive status in humans and experimental animals is associated with decreased immune response. Since monocyte chemotaxis and expression of CD11a are pivotal mechanisms in immune response, impairment of these events could explain the diminished immune response in depression.

Methods: To test this, rats were submitted to the forced swimming test (FST) for 3 and 15 days. Animals were sacrificed at days 4 (3 days' FST), 16 (15 days' FST) and 30 (15 days' FST and 15 days of recovery time). At these times, a blood sample was obtained for serum and leukocyte isolation. Mononuclear leukocytes were obtained by Histopaque gradient. Chemotaxis responsiveness was determined in Boyden chambers using zymosan-activated rat serum. Cellular CD11a expression and serum CD11a were determined by immunofluorescence and ELISA, respectively.

Results: Decreased chemotaxis was observed in FST animals at days 4 and 16 with total recovery at day 30. Diminished expression of cellular CD11a was observed at day 16 and remained decreased at day 30. There were no significant differences in serum CD11a content.

Conclusion: Decreased chemotactic response and expression of CD11a found in this experimental model of depression could be important mechanisms to induce impairment immune response in experimental and clinical depression.