Absence of CD4 impairs the efficiency of T cell receptor (TCR) signaling in response to major histocompatibility complex (MHC) class II–presented peptides. Here we use mice carrying a conditional Cd4 allele to study the consequences of impaired TCR signaling after the completion of thymocyte development. We show that loss of CD4 decreases the steady-state proliferation of T cells as monitored by in vivo labeling with bromo-deoxyuridine. Moreover, T cells lacking CD4 compete poorly with CD4-expressing T cells during proliferative expansion after transfer into lymphopenic recipients. The data suggest that T cells compete with one another during homeostatic proliferation, and indicate that the basis of this competition is TCR signaling.

Signal transduction in response to ligand recognition by T cell receptors regulates T cell fate within and beyond the thymus. Herein we examine the involvement of the CD4 molecule in the regulation of T helper cell survival. T helper cells that lack CD4 expression are prone to apoptosis and show diminished survival after adoptive transfer to irradiated recipients. The helper lineage in CD4 ؊/؊ animals shows a higher than normal apparent rate of cell division and is also enriched for cells exhibiting a memory cell phenotype. Thus the data point to a necessary role for CD4 in the regulation of T helper cell survival and homeostasis.

Background Children with chronic kidney disease (CKD) and their families deal with challenging circumstances. While numerous studies have shown that both patients and parents in these families can experience a variety of challenges and concerns, the experience of siblings is less well understood. The focus of this scoping review was on research addressing the experiences and well-being of siblings of children with CKD. Methods Following scoping review methodology, five databases were searched for peer-reviewed research or graduate theses published in English that addressed the experience or well-being of siblings aged 25 years or younger (biological, step or foster) of children with CKD; studies from any year or location were included. Two independent coders identified relevant studies. Findings were summarized and synthesized. Results Of the 2990 studies identified, 19 were chosen for full text review and eight fit the inclusion criteria. Five of the selected studies were qualitative, two were quantitative and one used mixed-methods. Four broad themes across studies were identified including family functioning, significant relationships, psychological well-being, and coping strategies. While there was some convergence between qualitative and quantitative findings, these linkages were weak. Conclusions Several unmet needs of siblings were uncovered by this review. Sibling perceptions of differential parental treatment and desire for information about CKD emerged as priorities for practice. Using a strength-based approach in order to better understand sibling experiences and well-being was also recommended for future research.

CD5 deficiency results in a hyper-responsive phenotype to Ag receptor stimulation. Here we show that the development and responses of CD4 lineage T cells are regulated by the function of CD5. Thymocytes expressing the I-Ad-restricted DO11.10 TCR undergo abnormal selection without CD5. In H-2d mice, the absence of CD5 causes deletion of double-positive thymocytes, but allows for efficient selection of cells expressing high levels of the DO11.10 clonotype. By contrast, there is enhanced negative selection against the DO11.10 clonotype in the presence of I-Ab. T cell hybridomas and DO11.10 T cells are more responsive to TCR stimulation in the absence of CD5. Such hypersensitivity can be eliminated by expression of wild-type CD5, but not by a form of CD5 that lacks the cytoplasmic tail. Finally, CD5 deficiency partially suppresses the block of CD4 lineage development in CD4-deficient mice. Taken together, the data support a general role for CD5 as a negative regulator of Ag receptor signaling in the development and immune responses of CD4 lineage T cells.

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