Fine antigen specificity of human γδ T cell lines (Vγ9+) established by repetitive stimulation with a serotype (KTH‐1) of a gram‐positive bacterium, Streptococcus sanguis

Abstract

We have established human γδ T cell lines specific for Streptococcus sanguis (S. sanguis) KTH‐1 present in normal oral cavity flora. The CD4⁻CD8⁻ CD3⁺Vγ9⁺Vδ1⁻CD45RO⁺ CD25⁺ T cell lines showed a proliferative response to the streptococcal antigen (Ag) in the presence of autologous antigen‐presenting cells without apparent evidence of HLA restriction. The proliferative response of the γδ T cell lines was completely blocked by anti‐TcRγδ monoclonal antibody (mAb) and anti‐HLA class I mAb (W6/32), whereas anti‐HLA classical class Ia mAb (B‐H9; anti‐HLA‐A,B,C), anti‐HLA class II mAb (anti‐DR, anti‐DQ, and anti‐DP) and anti‐CD4 mAb did not have any inhibitory effects. Surprisingly, the γδ T cell lines showed the proliferative response against the original bacterial Ag KTH‐1 exclusively, and exhibited no cross‐reactivity with nominal Ag such as purified protein derivative of tuberculin, tetanus toxoid and Mycobacterium tuberculosis, or the same species but different strain of S. sanguis, American Type Culture Collection (ATCC) standard strain (10556), or even with the same strain but different serotype of S. sanguis, KTH‐3. Moreover, cytokine production of the γδ T cell lines was similar to the Th1 pattern [interferon‐γ, tumor necrosis factor (TNF)‐α and TNF‐β]. They also produced interleukin‐8 that functions as one of chemoattractants for polymorphonuclear cells. Using direct sequencing technique of the polymerase chain reaction products, we found that junctional diversity of the T cell receptor (TcR) used by the parental KTH‐1 specific γδ T cell line and its subclones is rather limited. It is suggested that γδ T cells with canonical TcR could preferentially respond to KTH‐1 Ag. Thus, in addition to a broad or cross‐reactivity of γδ T cells against phylogenetically conserved stress/heat‐shock protein, which is well characterized by others, some peripheral blood γδ T cells could recognize and kill exogenous agents with fine antigenic specificity to protect the body against them.