I posted this the other day https://www.icmag.com/ic/showthread.php?t=371566
Immunoregulatory Role of Cannabinoids during Infectious Disease
Although the endocannabinoid system (ECS) is involved in the regulation of several physiological processes, including sleep and the immune response, its role during infections has not been fully studied. It is well known that the use of this drug increases susceptibility to infections because of the impact on the modulation of the immune system.
Concerning the medicinal or recreational use of marijuana, its influence on the course of an infection, whether this has been caused by bacteria, viruses, parasites, and to a lesser degree, fungi, has been reported. Furthermore, there is evidence suggesting the involvement of the ECS in the control and elimination of infectious agents such as bacteria, viruses, and some protozoa; in the case of fungi, few studies are available so far. The purpose of this review is to present the existing studies related to infections and the ECS, the microbicidal effects of compounds isolated from Cannabis sativa, and the association between marijuana use and the development of rare pathologies in specific diseases.
© 2017 S. Karger AG, Basel
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 . 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 . 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 . The observed results demonstrate that THC administration diminishes the immune response against the influenza virus.
It is well known that the immune system interacts with the nervous, immune, and endocrine systems, now considered as the neuroimmunoendocrine network. In this sense, ECS activation could be considered an important factor in the study of an effective or deficient immune response against infectious diseases. It should be highlighted that ECS activation might also present complex interactions during the course of an infection.
In this review, the in vitro evidence we have presented suggests that contact with cannabinoid compounds can affect different types of infectious agents, by allowing their replication or by eliminating them. This supports the idea of existing cannabinoid receptors infecting pathogens and that their activation may be responsible for previously mentioned effects, pointing to a new biological function of ECS activation. The immune system is responsible for dealing with foreign agents and their clearance, but, when the ECS is activated, the final result is sometimes different from what would be expected, i.e., the survival of infectious agents within the host.
In the case of bacteria, in vitro and in vivo tests present opposite effects, meaning that while in vitro studies showed cannabinoid compounds exerting antibacterial effects [6,30,54], in vivo tests showed increased host mortality. In the case of infection with L. pneumophila, this effect is due to immune system malfunction, caused by a compromised Th1 protective response  or because macrophage functions are inhibited , thereby supporting the notion that ECS activation contributes to the function of the immune system. Interestingly, when LPS was injected into mice, the results were similar to the results reported in vitro, because the lack of cannabinoid receptors induced an ineffective immune response [32,33].
Similarly, in the case of viral infections, the contact of viral particles with cannabinoid compounds makes them capable of negatively modulating some immune response parameters.
During HIV infection, there is a reduction in CD4+ T cells and IFN-γ concentration . During SIV infection, the activity of NK cells is inhibited , resulting in increased host mortality [63,65,66], and, in an influenza virus infection, the viral load is also increased
. In the studies in vitro, different cannabinoids increased HCV  and HSV replication [60,61]. On the other hand, the use of cannabinoids during an infection with Theiler's virus, an experimental model of MS, showed that cannabinoid agents such as WIN 5,212-2, ACEA, and JWH-015 may be good therapeutic targets for treating MS due to the fact that they promote remyelination .