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To the Editor: In their Research Letter, Dr Pacifici and colleagues¹ found that long-term users of cannabis had lower natural killer cell counts, lymphocyte proliferation, and levels of interleukin 2 (IL-2), as well as increased levels of IL-10 and transforming growth factor--1. The authors concluded that this pattern of results may reflect immunosuppressive properties of cannabis.

These results are the opposite of those we recently reported in a randomized, double-blind, placebo-controlled study among patients with multiple sclerosis.^2-3 We found that plant-derived cannabinoids promoted proinflammatory cytokine production (tumor necrosis factor and IL-12p40), with no change in lymphocyte proliferation, leukocyte subsets (CD4, CD8, CD14, CD15, CD16, CD19, CD45RA, CD45RO, and CD56), or other cytokines (IL-10 and IL-12p70).

We suspect that these divergent results reflect differences in the design of our study vs that of Pacifici et al. First, because their study was cross-sectional, their results may have reflected other confounding variables. . . . [Full Text of this Article]

Joep Killestein, MD, PhD; Bernard M. J. Uitdehaag, MD, PhD; Chris H. Polman, MD, PhD
Department of Neurology
VU Medical Center
Amsterdam, the Netherlands

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