CD2 can mediate TCR/CD3-independent T cell activation.
T lymphocytes can be activated clonotypically through TCR/CD3 complex or polyclonally via the CD2 molecule. Whether CD2-mediated activation is dependent on TCR/CD3 expression or signaling is controversial. We have re-explored this issue by using a series of CD2-transfected, TCR/CD3 surface membrane-negative human and mouse T cells. Our results clearly show that such T cells can be triggered for IL-2 secretion and increases in intracellular Ca2+ through the CD2 molecule in the absence of surface expression of TCR/CD3 complexes. These responses are only observed when cells express high levels of CD2 and there is a critical threshold of CD2 expression necessary for such activation in the absence of CD3. Concomitant expression of TCR/CD3 complex markedly lowers the level of CD2 required for activation via the latter pathway. These results provide a clear resolution of the controversy concerning the requirement for surface CD3 expression in T cell activation through CD2 and further suggest a possible role for CD2 in activation of TCR/CD3-negative cells.
Division of Molecular Genetics, School of Medicine, Chiba University, Japan.
H
H
Ohno
C
C
Ushiyama
M
M
Taniguchi
R N
RN
Germain
T
T
Saito
D015703:Antigens, CD / Q000502:physiology*; D000945:Antigens, Differentiation, T-Lymphocyte / Q000032:analysis / Q000502:physiology*; D018801:CD2 Antigens; D017252:CD3 Complex; D002460:Cell Line; D006801:Humans; D008213:Lymphocyte Activation; D011948:Receptors, Antigen, T-Cell / Q000032:analysis / Q000502:physiology*; D011971:Receptors, Immunologic / Q000032:analysis / Q000502:physiology*; D013601:T-Lymphocytes / Q000276:immunology*
D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; D018801:CD2 Antigens; D017252:CD3 Complex; D011948:Receptors, Antigen, T-Cell; D011971:Receptors, Immunologic