Question

The most relevant source of histamine in the immune system are:
(A). Red blood cells
(B). Basophils
(C). Mast cells
(D). Fiber
Choose the correct answer from the options given below:

• (A) and (B) only.
• (A) and (C) only.
• (B) and (C) only.
• (B) and (D) only.

Hint:

Mast cells and basophils are the "allergic alarm cells" of the body.
Their secretory granules are packed with histamine and heparin, which are released almost instantly during IgE-mediated allergic reactions.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Histamine is a biogenic amine involved in local immune responses, inflammatory cascades, and regulating physiological functions in the gut.
It acts as a primary mediator of immediate hypersensitivity (allergic) reactions.

Step 2: Detailed Explanation:
In the immune system, histamine is synthesized and stored in specialized granules within specific immune cells.
The two primary cellular sources of histamine are:
- (C) Mast cells: These are tissue-resident granulocytes located in mucosal and connective tissues, especially near blood vessels and nerves.
- (B) Basophils: These are circulating granulocytes that represent a small fraction of white blood cells.
Both mast cells and basophils express high-affinity IgE receptors ($\text{Fc}\epsilon\text{RI}$) on their surfaces.
When allergen-specific IgE molecules bound to these receptors are cross-linked by an antigen, it triggers a rapid degranulation process.
During degranulation, the preformed histamine stored inside their cytoplasmic granules is rapidly released into the extracellular environment, causing vasodilation, increased capillary permeability, and smooth muscle contraction.
Red blood cells (A) and fibers (D) do not synthesize or store histamine.

Step 3: Final Answer:
Therefore, the most relevant sources of histamine are Basophils and Mast cells, which corresponds to option (C).