Immunological mechanisms through the activation of CD4-positive T-cells have been assumed to be involved in the pathogenesis of giant cell arteritis (GCA). Many studies employing frozen tissues of temporal artery biopsy, peripheral blood lymphocytes, and plasma of GCA patients have revealed the contribution of interferon-γ and interleukin-17 in both protein and mRNA levels. However, the analyses using formalin-fixed and paraffin-embedded (FFPE) tissue specimens, in which the correlation between histopathologic pictures and immunological circumstances would be elucidated, have been limited. Here, we performed the immunohistochemical analyses of infiltrating small lymphocytes in GCA lesions using FFPE specimens, especially of the subsets of CD4-positive T-cells by immunohistochemistry with antibodies against T-bet, GATA-3, RORγT, and Foxp3, which is the differentiation-specific transcription factor for Th1, Th2, Th17, and Treg cells, respectively. In these slides, the nuclear-positive staining is much more clearly and easily identifiable than the cytoplasmic staining for cytokines. The results indicate the predominance of T-bet-positive Th1 cells in infiltrating T-cells in most of active arteritis lesions of GCA. Furthermore, our data suggest the possible immunosuppressive microenvironment induced by T-reg cells and M2-type macrophages in the arteritis lesions throughout the course of GCA inflammation.