Severe combined immunodeficiencies (SCIDs) are characterized by a lack of which of the following?

Severe combined immunodeficiencies (SCIDs) are characterized by a profound defect in both T cells and B cells, leading to a severely compromised adaptive immune response. In many forms of SCID, the lack of functional T cells is a critical component that results in the inability to orchestrate an effective immune response against infections. Individuals with SCID are particularly vulnerable to opportunistic infections due to the absence of T cells, which play a crucial role in cell-mediated immunity, as well as helping B cells produce antibodies.

While B cells are also absent or non-functional in certain types of SCID, the emphasis on T cell deficiency is typically highlighted because T cells are central to initiating and coordinating the immune response. In some variations of SCID, such as those related to adenosine deaminase deficiency, both T and B cell levels are severely impaired. Thus, choosing T cells reflects the critical aspect of how SCID manifests clinically, primarily through the lack of this specific cell type involved in both adaptive immunity and in supporting B cell function.

The other cell types mentioned can be important for certain immune functions, but the hallmark and most devastating aspect of SCID is the absence of functional T cells, which fundamentally disrupts the entire immune