Introduction: This study evaluated depression, monocyte phenotype, and immune function in physically active cannabis users. Methods: Participants (N = 23) were classified as either cannabis users (CU, n = 11) or non-users (NU, n = 12). White blood cells isolated from blood were analyzed for co-expression of cluster of differentiation 14 and 16 using flow cytometry. Lipopolysaccharide (LPS) was cultured with whole blood and assessed for interleukin-6 and tumor necrosis factor-α (TNF-α) release. Results: The percentage of white blood cells classified as monocytes was not different between groups; however, CU had a significantly greater percentage of monocytes classified as intermediate (p = 0.02). When standardized per milliliter of blood, CU had significantly greater numbers of total monocytes (p = 0.01), classical monocytes (p = 0.02), and intermediate monocytes (p = 0.01). Intermediate monocytes per milliliter of blood were positively correlated to the number of times CU used cannabis per day (r = 0.864, p < 0.01) and Beck Depression Inventory-II (BDI-II) score (r = 0.475, p = 0.03), which was significantly greater in CU (5.1 ± 4.8) compared with NU (0.8 ± 1.0; p < 0.01). CU released significantly less TNF-α per monocyte in response to LPS. Conclusions: CU had altered monocyte phenotypes and functions compared with NU. Elevations in intermediate monocytes were positively correlated with measures of cannabis use and BDI-II score.
Keywords: depression; immune function; inflammation; innate immunity; marijuana.