Defective recruitment and activation of ZAP-70 in common variable immunodeficiency patients with T cell defects.
We have previously identified a subset of common variable immunodeficiency (CVID) patients with defective T cell function associated with impaired activation of the TCR-dependent tyrosine phosphorylation cascade. Here we have assessed the structural and functional integrity of the principal components involved in coupling the TCR/CD3 complex to intracellular tyrosine kinases in two of these patients. We show that ZAP-70 fails to bind the signaling-competent CD3zeta tyrosine phosphorylation isoform and to become activated following TCR engagement, suggesting that defective recruitment of ZAP-70 might underlie the TCR signaling dysfunction in these patients. Determination of the nucleotide sequences encoding the intracellular domains of the CD3/zeta subunits and ZAP-70 did not reveal any mutation. Furthermore, ZAP-70 from these patients could interact in vitro with recombinant phospho-zeta, ruling out genetic defects at the immunoreceptor tyrosine-based activation motif/SH2 domain interface responsible for ZAP-70 recruitment to the activated TCR. No defect was found in expression, activity or subcellular localization of Lck, which is thought to be primarily responsible for CD3zeta phosphorylation. Hence, while the T cell defect in these CVID patients can be pinpointed to the interaction between ZAP-70 and CD3zeta, the integrity in the components of the signaling machinery involved in this process suggests that additional components might be required for completion of this step.
Boncristiano
M
M
Department of Evolutionary Biology, University of Siena, Italy.
Majolini
M B
MB
D'Elios
M M
MM
Pacini
S
S
Valensin
S
S
Ulivieri
C
C
Amedei
A
A
Falini
B
B
Del Prete
G
G
Telford
J L
JL
Baldari
C T
CT
D000818:Animals; D017074:Common Variable Immunodeficiency / Q000276:immunology*; D006801:Humans; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck) / Q000032:analysis; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000502:physiology*; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism / Q000502:physiology*; D013601:T-Lymphocytes / Q000502:physiology*; D051746:ZAP-70 Protein-Tyrosine Kinase
D008565:Membrane Proteins; D011948:Receptors, Antigen, T-Cell; C054979:antigen T cell receptor, zeta chain; D011505:Protein-Tyrosine Kinases; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D051746:ZAP-70 Protein-Tyrosine Kinase; C497261:ZAP70 protein, human; C497262:Zap70 protein, mouse