August 02, 2012

Q&A: Cells Involved in Inflammatory and Allergic Reactions

The innate immune system constitutes the first-line barrier, the rapid-response mechanism, to prevent microbial invasion. Its components are inherited from parent to child and directed against molecules expressed only by micro-organisms. These host defense components are evolutionarily ancient, found in all multicellular organisms, and expressed in humans as conserved elements (homologs) shared with other vertebrates and, in some form, with insects and plants.

This article is for Medical Students & Professionals
This is a Question & Answer revision article designed for medical students and professionals preparing for the PLAB, MRCP or USMLE examinations. They are based on actual questions from these examinations. You may find the Allergies & Allergic Reactions article more useful, or one of our many articles on Diseases & Conditions, Medical Syndromes, Health & Wellness or Home Remedies.
In this article:
Cells of the innate immune system
MCQ: clinical scenario
MCQ: answer
MCQ: explanation

Cells of the innate immune system

"Professional" phagocytes (neutrophils, monocytes, macrophages) represent the critical effector component of the innate immune system. Other cell types, including epithelial cells, eosinophils, mast cells, and platelets, express pattern recognition receptors (PRRs), including toll-like receptors (TLRs), and play an important contributory role in innate host defense. Dendritic cells express PRRs, and as principal antigen-presenting cells, they serve to link innate and adaptive immunity.

MCQ: clinical scenario

A certain type of cell plays a central role in inflammatory and immediate allergic reactions and settles in connective tissues and usually does not circulate in the blood stream.

This type of cell is known as a:

a) Basophil
b) Mast cell
c) Eosinophil
d) Neutrophil
e) Macrophage

MCQ questions & answers on

MCQ: answer

The correct answer is B

MCQ: explanation

Mast cells and basophils play a central role in inflammatory and immediate allergic reactions. They are able to release potent inflammatory mediators, such as histamine, proteases, chemotactic factors, cytokines and metabolites of arachidonic acid that act on the vasculature, smooth muscle, connective tissue, mucous glands and inflammatory cells.

Mast cells settle in connective tissues and usually do not circulate in the blood stream. Basophils are the smallest circulating granulocytes with relatively the least known function. They arise in the bone marrow, and following maturation and differentiation, are released into the blood circulation. If they are adequately stimulated they may settle in the tissues.

1). UpToDate: An overview of the innate immune system. Available online:

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