Introduction to the symposium on alcohol and T-cell immunity

Immune correlates of depression

The relation of depression to immunological assays is complex and variable. However, meta-analyses have demonstrated that depressed subjects are likely to show changes in several immune assays. Depressed subjects are likely to have changes in major immune cell classes with an increase in total white blood cell counts and a relative increase in numbers of neutrophils. However, the relative number of lymphocytes is likely to be reduced in depressed subjects. Depression also appears to be associated with increases in at least one measure of immune activation, although further investigations are clearly needed to replicate these interesting observations. Finally, depression is reliably associated with a suppression of mitogen-induced lymphocyte proliferation and with a reduction of NK activity. Despite the heterogeneity of findings, the effect sizes in the relationship between depression and lymphocyte proliferation and NK activity are large as compared to those observed in other areas of psychological and medical research. Several moderating factors may explain and account for the heterogeneity that has been found in the depression-immune results. Future immunologic studies in depressed subjects are needed to clarify the effects of gender and reproductive hormones on the relation between depression and immunity. Severity of melancholic symptoms and sleep disturbance appear to moderate the immune changes in depression but the biological mechanisms that account for the link between these neurovegetative symptoms and depression are not yet known. Finally, assessment of co-morbidity in depressed subjects deserves an increased focus. Data generated from our laboratory clearly show that assessment of alcohol- and tobacco dependence is critical in the interpretation of immune changes in depressed subjects. The clinical significance of changes in immune responses in depressed subjects remains an unanswered question. Studies that use immune measures with disease specific endpoints, as has been recently conducted in the study of VZV immune responses, would help identify the possible link between depression, immune system alterations, and health outcomes.

Ethanol-induced osmolality changes and lymphocyte proliferation

While there have been reports on the in vitro effects of ethanol on mitogen-stimulated lymphocyte proliferation, little attention has been paid to whether these effects are mediated by the ethanol molecule per se or the associated hyperosmolality. There is controversy whether ethanol at high concentrations inhibits or has no effect on mitogen-stimulated proliferation of T cells. In this study we sought to distinguish between effects due to ethanol and those related to increased osmolality. Rat splenocytes were cultured in vitro in hypertonic (320 mOsm) or isotonic (320 mOsm) ethanol solutions (up to 400 mg/dL), or in corresponding hypertonic solutions without ethanol. Proliferative responses to the B cell mitogen lipopolysaccharide and the T cell mitogen concanavalin A were measured by mitochondrial dimethylthiazole diphenyl tetrazolium metabolism and [(3) H]-thymidine incorporation into DNA. B cell response was not significantly affected by ethanol under any conditions. By contrast, T cell proliferative responses were significantly inhibited by isotonic ethanol solutions or hypertonic solutions in the absence of ethanol, but not by hypertonic ethanol solutions. These results indicate that, while high osmolality is normally inhibitory to lymphocyte function, the increase in osmolality caused by ethanol is protective against the otherwise detrimental effects of ethanol.

Biphasic in vivo immune function after low- versus high-dose alcohol consumption

A series of experiments was performed to assess the alterations in immune status in vivo that are associated with differences in the amount and duration of ethanol intake. Using a nonspecific delayed cutaneous hypersensitivity-like response to the intradermal injection of phytohemagglutinin, the area of induration (skin test response) was significantly enhanced (p = 0.008) after low-dose ethanol (0.5 g/kg) administered daily by gastric gavage for 5 days. High-dose ethanol (6.0 g/kg) significantly diminished this response (p = 0.03). Using an experimental model of Mycobacterium bovis hepatitis, the host immune response was also altered in a biphasic manner after chronic, 28-day ethanol consumption. With this model 0.43 +/- 0.03 g/kg/day (mean +/- SEM) of ethanol (low dose) was associated with a 40% improvement in the removal of the organisms from liver tissue (p = 0.002). High dose (12.1 +/- 0.5 g/kg/day) impaired removal, resulting in a 55% increase in the number of viable organisms (p = 0.001). The levels of three cytokines, MIF, TNF-alpha, and IL-2, known to be involved in the modulation of the host response to mycobacterial infections, were measured in sera after the infection. The serum levels of these cytokines in response to infection did not correlate with this biphasic response to different alcohol dose levels.