Influenza
The administration of THC could be harmful for a host infected with the influenza virus. As reported in studies on mice, THC administration after an immune challenge with influenza virus A/PR/8 resulted in increased viral loads, higher hemagglutinin 1 expression, and diminished CD4+ and CD8+ lymphocyte and macrophage recruitment into the lungs [77]. Some of these effects were observed in an opposite manner when CB1 and CB2 knockout mice were infected, i.e., showing increased CD4+ lymphocyte recruitment, IFN-γ levels, and lung inflammation, higher than in control WT mice [78]. Other immune parameters affected include cytokine secretion by CD4+ T cells and NK cells, besides a lower overall percentage of subpopulations of antigen-presenting cells present in the lungs of infected mice [79]. The observed results demonstrate that THC administration diminishes the immune response against the influenza virus.