Which term best describes a small peptide formed during complement activation that causes increased vascular permeability, contraction of smooth muscle, and release of histamine from mast cells?

The term that best describes a small peptide formed during complement activation, which causes increased vascular permeability, smooth muscle contraction, and the release of histamine from mast cells, is anaphylatoxin. During the complement cascade, certain components such as C3a and C5a are generated. These peptides play a critical role in the immune response by mediating inflammatory effects, including promoting vascular changes and recruiting immune cells to sites of injury or infection.

Anaphylatoxins are specifically known for their ability to enhance vascular permeability, thereby allowing plasma proteins and immune cells to move more easily from the bloodstream into tissues where they are needed for the immune response. The contraction of smooth muscle can lead to bronchoconstriction, which is significant in conditions such as asthma. Additionally, their role in stimulating mast cells to release histamine contributes to the inflammatory response.

Understanding the function of anaphylatoxins is crucial in immunology and can help in comprehending various allergic and inflammatory conditions.