**Question:** Allergic asthma and rhinitis are related to the chemokine receptor:

A. ChemR23
B. CCR3
C. CCR4
D. CCR5

**Core Concept:** Chemokines are small proteins that play a crucial role in the recruitment of leukocytes to the site of inflammation, particularly in allergic disorders like asthma and rhinitis. Chemokine receptors are G protein-coupled receptors that bind to specific chemokines and initiate cellular responses.

**Why the Correct Answer is Right:** Chemokine receptors are essential in mediating the effects of chemokines, which are involved in the recruitment of leukocytes (white blood cells) to sites of inflammation. In allergic asthma and rhinitis, the recruitment of eosinophils, neutrophils, and lymphocytes is crucial for the pathogenesis of these conditions.

**Why Each Wrong Option is Incorrect:**

A. ChemR23 (ChemR23) is a chemokine receptor involved in regulating bone marrow homing of stem cells and the immune response to lipopolysaccharide. It is not related to the recruitment of leukocytes in allergic asthma and rhinitis.

B. CCR3 (Chemokine (C-C motif) receptor 3) is a chemokine receptor involved in mediating the recruitment of eosinophils and basophils, which are essential in the pathogenesis of allergic asthma and rhinitis.

C. CCR4 (Chemokine (C-C motif) receptor 4) is involved in the recruitment of T helper cells and Th2 cells, which play a role in the allergic response. However, it is not specifically associated with allergic asthma and rhinitis.

D. CCR5 (Chemokine (C-C motif) receptor 5) is involved in the recruitment of monocytes, macrophages, and T cells, but it is not primarily associated with allergic asthma and rhinitis.

**Clinical Pearl:** Allergic asthma and rhinitis are characterized by type 2 inflammation, which involves eosinophils, neutrophils, and lymphocytes. Chemokine receptors, particularly CCR3, play a vital role in the recruitment and activation of these cells at the site of inflammation, making CCR3 the correct answer.