Enhanced Humoral Immunity in Mice Lacking CB1 and CB2 Receptors (cnr1 −/− /cnr2 −/− Mice) is Not Due to Increased Splenic Noradrenergic Neuronal Activity

Peripheral sympathetic noradrenergic neurons originating in the celiac mesenteric plexus have axons that terminate in close proximity to antibody-producing B cells in the spleen. Norepinephrine (NE) released from these neurons is reported to augment antibody production in response to an immune challenge via an action at the β2-adrenergic receptor (β2AR). Cannabinoids are immunosuppressive, and mice lacking CB1 and CB2 receptors (Cnr1 −/− /Cnr2 −/− mice) have augmented cell-mediated immune responses. The purpose of this study was to determine if Cnr1 −/− /Cnr2 −/− mice also exhibit enhanced humoral immunity and if that is associated with corresponding changes in noradrenergic neurons terminating in the spleen. The results reveal that IgM and IgG are enhanced in Cnr1 −/− /Cnr2 −/− mice as compared to WT both in immunologically naïve and lipopolysaccharide (LPS)-treated mice. While the elevated antibody production was correlated with increased expression of β2AR on splenic B cells and increased splenic capsule NE concentrations, the activity of noradrenergic neurons was suppressed in spleens from Cnr1 −/− /Cnr2 −/− mice as compared with WT controls. Together, these results suggest that Cnr1 −/− /Cnr2 −/− mice exhibit enhanced NE vesicular storage in axon terminals in these neurons, which might limit the NE available to bind β2AR on target cells, such as B cells. The results also demonstrate that enhanced antibody responses in the absence of CB1 and CB2 receptors are not due to increased sympathetic noradrenergic neuronal activity in the spleen.