The ability of a single cytokine to alter the expression of several genes is called

• A. redundancy.
• B. pleiotropy.
• C. autocrine stimulation.
• D. endocrine effect.

Answer: (B)

Pleiotropy is when a single cytokine can influence multiple genes and produce several distinct effects. A cytokine can act on different cell types or activate several signaling pathways, leading to coordinated changes in the expression of a variety of genes. This is why one cytokine can drive different outcomes in different tissues or contexts, such as promoting antibody production in B cells while also affecting T cell differentiation or liver protein synthesis.

Autocrine stimulation refers to a cytokine acting on the same cell that secreted it, not to multiple gene targets. Endocrine effect describes distant action through the bloodstream, which is about distance rather than the number of gene targets. Redundancy means overlapping functions among different cytokines, not that a single cytokine alters many genes.