ABSTRACT
BACKGROUND: Cytomegalovirus (CMV) infection during fetal life causes severe symptoms and is associated with prolonged viral excretion. Previous studies reported low CD4(+) T-cell responses to CMV infection in early life, contrasting with large responses of effector CD8(+) T cells. The mechanisms underlying the defective CD4(+) T-cell responses and the possible dissociation with CD8(+) T-cell responses have not been clarified. METHODS: The magnitude and the quality of the fetal CD8(+) and CD4(+) T-cell responses to CMV infection were compared to those of adults with primary or chronic infection. RESULTS: In utero CMV infection induced oligoclonal expansions of fetal CD4(+) and CD8(+) T lymphocytes expressing a T-helper type 1 or Tc1 effector phenotype similar to that of adult CMV-specific cells. However, the effector cytokine responses and the polyfunctionality of newborn CD4(+) and CD8(+) T cells were markedly lower than those of adult cells. This reduced functionality was associated with a higher expression of the programmed death 1 inhibitory receptor, and blockade of this receptor increased newborn T-cell responses. CONCLUSIONS: Functional exhaustion limits effector CD4(+) and CD8(+) T-lymphocyte responses to CMV during fetal life.
Subject(s)
CD4-Positive T-Lymphocytes/immunology , CD8-Positive T-Lymphocytes/immunology , Cytomegalovirus Infections/congenital , Cytomegalovirus Infections/immunology , Cytomegalovirus/immunology , Pregnancy Complications, Infectious/immunology , Adult , Antigens, Viral/immunology , CD4-Positive T-Lymphocytes/cytology , CD8-Positive T-Lymphocytes/cytology , Cohort Studies , Cytokines/blood , Cytokines/immunology , Female , Fetal Blood/cytology , Humans , Infant, Newborn , PregnancyABSTRACT
The generation of high-affinity antibodies and the development of B cell memory are dependent on the help provided by CD4 T cells. Mouse studies indicate that STAT3 signaling in CD4 T cells promotes the acquisition of the B cell help function. However, the role of STAT3 in humans has been controversial. In this study, we show that IL-6 and other STAT3 activating cytokines (IL-21 and IL-27) induce the differentiation of CD4 T cells promoting antibody production by B cells. The acquisition of B cell stimulating properties by naive cord blood CD4 T cells required the STAT3-dependent expression of ICOS and IL-21. Gene reporter and ChIP experiments unambiguously demonstrated that upon IL-6 stimulation, STAT3 induces the transcription of the ICOS gene through direct recruitment to the proximal promoter region indicating that STAT3 acts in part through the direct activation of the ICOS gene.
