Alcohol Use Disorder (AUD) is a disease with multiple associated complications. The immune system can be compromised by alcohol abuse and alterations of the innate and adaptive immunity may predispose to the development of infections. Related to the acquired immunity, chronic alcohol consumption has been associated with alterations in the number, function and phenotype of B and T lymphocytes. The aim of this Thesis is to better characterize the alterations of T lymphocyte subsets in patients with AUD. The results obtained in this research have been published as original articles in the journal Drug and Alcohol Dependence. In the first article, we aimed to analyze the prevalence and factors associated with quantitative alterations of T lymphocytes subpopulations in 238 patients admitted to treatment of AUD between 2002 and 2012. Specifically, CD4+, CD8+, Double Positive (CD4+/CD8+) and Double Negative (CD4-/CD8-) lymphocytes are analyzed in this case series. The results show that quantitative T-cell alterations are frequent and, in fact, 25% of patients have increased numbers of CD8+, 50% have low Double Negative cells and 13% have decreased number of CD4+ cells. Therefore, the article discuss the importance of including the analysis of the T-cell subpopulations in individuals with chronic AUD to better identify those at high risk of infections. The second article focuses on markers of LT activation when comparing their expression in AUD patients and healthy controls. We used a combination of cell surface markers (CD38 and HLA-DR). Results show that patients with AUD have an excess of CD8+ T-cell activation compared to healthy controls and that the excess of activation is inversely correlated with the absolute number of CD4+ lymphocytes.