Published online before print September 12, 2008
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
9-tetrahydrocannabinol

,1
* Center for Integrative Toxicology, Cell and Molecular Biology Program, and
Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan, USA
1 Correspondence: Center for Integrative Toxicology and Department of Pharmacology and Toxicology, Michigan State University, 315 National Food Safety and Toxicology Building, East Lansing, MI 48824-1317, USA. E-mail: kamins11{at}msu.edu
The role of cannabinoid receptors, CB1 and CB2, in immune competence and modulation by
9-tetrahydrocannabinol (
9-THC) was investigated in CB1–/–/CB2–/– mice. Immunofluorescence analysis of splenic leukocytes showed no significant differences in the percentage of T cell subsets, B cells, or macrophages between wild-type and CB1–/–/CB2–/– mice. Lymphoproliferative control responses to PHA, phorbol ester plus ionomycin, or LPS and sensitivity to suppression by
9-THC showed no profound differences between the two genotypes, although some differences were observed in control baseline responses. Likewise, similar control responses and sensitivity to
9-THC were observed in mixed lymphocyte responses (MLR) and in IL-2 and IFN-
production in both genotypes. Conversely, humoral immune responses showed a markedly different profile of activity.
9-THC suppressed the in vivo T cell-dependent, anti-sheep RBC (anti-sRBC) IgM antibody-forming cell (AFC) response in wild-type but not in CB1–/–/CB2–/– mice, and the in vitro anti-sRBC IgM response in CB1–/–/CB2–/– splenocytes was too low to rigorously assess CB1/CB2 involvement in modulation by
9-THC. Conversely, comparable in vitro IgM AFC control responses to LPS and CD40 ligand (CD40L) activation were observed in the two genotypes. Interestingly, LPS-induced IgM responses were refractory to suppression by
9-THC, regardless of genotype, and CD40L-induced IgM responses were only suppressed by
9-THC in wild-type but not in CB1–/–/CB2–/– B cells. Collectively, we demonstrate differential involvement of CB1 and/or CB2 in immune modulation by
9-THC and in some control responses. Moreover, CB1/CB2 involvement was observed in humoral responses requiring CD40-initiated signaling for suppression by
9-THC.
Key Words: immunopharmacology CD40 ligand humoral immunity cell-mediated immunity