Lymphocytic Subpopulation Profiles in Bronchoalveolar Lavage Fluid and Peripheral Blood From Tobacco and Marijuana Smokers: Discussion
Such immmunoregulatory abnormalities may contribute to disturbances of pulmonary defense mechanisms manifested by the predisposition to malignancy and infection. Our data suggest that these lymphocytic subpopulation alterations do not occur with marijuana use or are too small to be detected within our sample size.
The information currently available allows only speculative explanations for differences in bronchoalveolar T-lymphocyte subpopulation profiles between MS and TS. Several factors may play a role. First, constituents in tobacco smoke responsible for changes leading to lower BAL CD4 percentages and CD4:CD8 ratios may be absent or present in smaller amounts in marijuana smoke. Second, marijuana smoke may contain substances that counteract some of these local pulmonary effects. Our data would support this possibility in that there was a significant interaction between tobacco and marijuana effects on bronchoalveolar CD4 percentage and the relative proportion of CD4 and CD8 cells in which the tobacco effect was less pronounced in marijuana users. Finally, differences in quantity and pattern of cumulative exposure to tobacco smoke as compared with marijuana smoke may lead to different immunologic effects. Canadian helth& care mall read only The psychoactive effects of marijuana would discourage even heavy habitual users from smoking amounts of marijuana comparable to the quantity to tobacco consumed by the tobacco smokers examined in this study. It is possible that more intense exposure to marijuana smoke would have effects on bronchoalveolar lymphocytic subpopulations similar to those of tobacco.
Both marijuana and tobacco were associated with higher bronchoalveolar B-lymphocytic concentrations, although the increase was statistically significant only among the users of both substances compared with NS. Whether accumulation of В cells in the lower respiratory tract contributes to the local inflammatory changes that occur with marijuana and tobacco use would be of interest.
Our study also found marijuana and tobacco to have different effects on circulating T-lymphocyte subpopulations. Marijuana, but not tobacco use, was associated with increased percentages of CD4 cells, decreased percentages of CD8 cells, and elevated CD4:CD8 ratios in PB. Contrary to this observation, several previous reports have suggested that tobacco smoking is associated with altered circulating T-lymphocytic phenotypic profiles. Heavy TS have been noted to have reduced PB CD4 cell percentages compared with NS. Other studies that have examined large numbers of TS with varying amounts of consumption have reported a small, but statistically significant increase of CD4 cell percentage, and the CD4:CD8 ratio. In this study and another published previously, we also measured slightly higher CD4 cell percentages in TS, but the difference was not statistically significant. It is possible that in our smaller sample, we missed a significant difference due to a type II error. Thus, the difference we observed between marijuana and tobacco effects on percentage of PB CD4 cells may have been one of magnitude, rather than mechanism.
The practical significance of a study that examines cellular characteristics is dependent on the associated clinical impact. Immunologic alterations that have been observed in TS are of potential importance because of the correlation with well-documented adverse health effects. The present study suggests that frequent marijuana use may not have the same consequences on lung health as those from tobacco smoking. Understanding the importance of the cellular effects of marijuana will require additional epidemiologic information relating to the incidence of malignancy or infection in habitual marijuana users.