Defective signal transduction by the CD2 molecule in immature T-cell receptor/CD3- thymocytes.
The CD2 accessory molecule mediates an activation pathway in mature T cells, transducing signals similar to those observed following stimulation of the T-cell receptor/CD3 (TCR/CD3) complex. CD2 is also one of the earliest cell surface markers to appear during thymic ontogeny and has been proposed to be a stimulatory pathway for immature thymocytes that have not yet expressed TCRs on their surface (TCR/CD3-). To examine this hypothesis highly purified TCR/CD3- human thymocytes were stimulated using mitogenic combinations of anti-CD2 monoclonal antibodies or individual biotinylated anti-CD2 monoclonal antibodies crosslinked with avidin. TCR/CD3+ thymocytes responded readily to either stimulus as determined by anti-phosphotyrosine immunoblotting, and the pattern of tyrosine phosphorylated substrates was similar to that of mature T cells. In contrast, TCR/CD3- thymocytes responded weakly and with a distinct substrate pattern. In addition, the altered signal transduced by CD2 in TCR/CD3- thymocytes did not lead to a rise in intracellular calcium, failed to induce interleukin 2 receptor expression, and did not serve as a comitogen with phorbol ester or interleukin 2, functions that were all intact in TCR/CD3+ thymocytes. Failure of TCR/CD3- thymocytes to respond to CD2 stimulation was not due to an intrinsic defect in these cells as they responded normally to phorbol ester plus calcium ionophore. In TCR/CD3- thymocytes, CD2 stimulation also failed to affect steady-state mRNA levels of the recombination-activating genes RAG1 and RAG2, whereas in TCR/CD3+ cells activation of the CD2 pathway terminated their expression. Together, these data support the concept that CD2 engagement does not deliver a stimulus to TCR/CD3- thymocytes and suggests that this molecule may not directly participate in the earliest stages of thymic development.
Turka
L A
LA
Department of Medicine, University of Michigan, Ann Arbor 48109.
Fletcher
M C
MC
Craighead
N
N
Thompson
C B
CB
June
C H
CH
D000945:Antigens, Differentiation, T-Lymphocyte / Q000502:physiology*; D018801:CD2 Antigens; D017252:CD3 Complex; D002118:Calcium / Q000502:physiology; D002478:Cells, Cultured; D002675:Child, Preschool; D015870:Gene Expression; D005796:Genes; D006801:Humans; D066298:In Vitro Techniques; D008213:Lymphocyte Activation; D010766:Phosphorylation; D019000:Phosphotyrosine; D012333:RNA, Messenger / Q000235:genetics; D011948:Receptors, Antigen, T-Cell / Q000502:physiology*; D011971:Receptors, Immunologic / Q000502:physiology*; D015375:Receptors, Interleukin-2 / Q000235:genetics / Q000378:metabolism; D011995:Recombination, Genetic; D015398:Signal Transduction; D016176:T-Lymphocyte Subsets / Q000502:physiology*; D013950:Thymus Gland / Q000166:cytology; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism
D000945:Antigens, Differentiation, T-Lymphocyte; D018801:CD2 Antigens; D017252:CD3 Complex; D012333:RNA, Messenger; D011948:Receptors, Antigen, T-Cell; D011971:Receptors, Immunologic; D015375:Receptors, Interleukin-2; D019000:Phosphotyrosine; D014443:Tyrosine; D002118:Calcium