Complement receptors (CR)

Author: V. Dimov, M.D., Allergist/Immunologist and Assistant Professor at University of Chicago
Reviewer: S. Randhawa, M.D., Allergist/Immunologist

There are 4 types of complement receptors (CR):

- CR1 (CD35) promote phagocytosis of antigens coated by complement fragments
- CR2 (CD21) connect the innate and adaptive immune systems through humoral response
- CR3 (Mac-1, CD11b/CD18) (integrin receptors) promote both phagocytosis and leukocyte adhesion
- CR4 (gp 150/95, CD11c/CD18) is a market for dendritic cells

To remember: CR3 (CD11b/CD18) and CR4 (CD11c/CD18) are affected in LAD type I.

CD55 (DAF) and CD59 are affected in PNH. Eculizumab (Soliris) is a humanized mAb against complement protein C5. It is used for treatment of paroxysmal nocturnal hemoglobinuria (PNH).

Complement receptor 2 (CR2/CD21) is part of the B-cell coreceptor and expressed by mature B cells and follicular dendritic cells. CD21 is a receptor for C3d-opsonized immune complexes and enhances antigen-specific B-cell responses. Viruses, such as HIV and EBV, use the complement receptors (CR2) to the enter the cell. Genetic CD21 deficiency is associated with hypogammaglobulinemia (JACI, 2011).

Complement receptors (click to enlarge the image).

All of the following are correct pairings of complement receptors and function except:

A. CR1 (CD35) with phagocytosis, immune complex clearance
B. CR4 with phagocytosis
C. CR3 with EBV receptor, leukocyte adhesion, phagocytosis
D. CR2 (CD21) with B cell activation, trapping of antigens in germinal centers

Answer: C. EBV use CR2 (CD21) to enter the cell.

Place in increasing order the CD designation of complement receptors CR1, CR2, CR3, CR4:

A. CD21, CD35, CD11b/CD18, CD11c/CD18
B. CD35, CD21, CD11b/CD18, CD11c/CD18
C. CD35, CD21, CD11c/CD18, CD11b/CD18
D. CD11b/CD18, CD11c/CD18, CD21, CD35

Answer: B.

Deficiency of which component of the complement is among the causes of paroxysmal nocturnal hemoglobinuria (PNH)?

A. CR2 (CD21)
B. Factor I

Answer: C.


Allergy and Immunology MKSAP, 3rd edition.
Chapter 2. Innate immunity. Abbas et al: Cellular & Molecular Immunology, 6th Ed.

Published: 09/05/2010
Updated: 10/02/2011

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