Actinobacillus (Aggregatibacter) actinomycetemicomitans is a bacterium that plays important role in Periodontitis. Recent publications have correlated AaGroEL (A.actinomycetemcomitans GroEL Protein) protein with periodontal pathologies however, how does this protein affect T lymphocytes and the profile of T lymphocytes. immune response, are not reported yet. Within this thesis project, AaGroEL protein is produced as its recombinant form. The effects of AaGroEL protein, after it is obtained, have been investigated on naive T lymphocytes in peripheral blood. In this research, the proliferative and activating effects of AaGroEL protein on T lymphocytes were determined by investigating the expression of CD25 and CD69 cell surface molecules. AaGroEL protein has an effect on CD4+ T lymphocytes and depending on time, it increases CD25 and CD69 expression. Additionally, it was found that, CD4+CD25+T cells are negative for FOXP3. The cytokines of CD4+ T lymphocytes were profiled. Firstly, the cytokines that were released by PBMC.s on culture supernatant were determined. Following AaGroEL stimulation, IL-6, IL-10, IFNg ve TNF. were secreted to the supernatant. Intracellular cytokine staining was applied to determine the source of those cytokines which was found that CD4+ T cells produce those cytokines as well as nonlymphocytes and B or/and CD8+ cells also secrete them. IL-2 was secreted by CD4+ T lymphocytes only. These findings have demonstrated us; AaGroEL protein activates naive CD4+ T cells towards Th1 response. In conclusion, AaGroEL protein has an antigenic effect on T lymphocytes, regulates immune response and play important role on periodontal pathology.