Page 57 - Concise Pathology for Exam Preparation ( PDFDrive )

42 SECTION I General Pathology

Q. Write briefly on chemokines.

Ans. Chemokines are a family of small, 8–10 kD proteins that act primarily as chemoat-
tractants for specific leukocytes.
• They bind to seven transmembrane G protein–coupled receptors.
• There are 40 different types of chemokines and 20 different types of receptors.
• Chemokines are classified into four groups based on the arrangement of conserved
cysteine residues in the proteins, namely,
1. CXC chemokines or a-chemokines
(a) One amino acid residue separates first two conserved cysteine residues.
(b) Typical example is IL8. IL8 is secreted by macrophages and endothelial cells and
primarily acts on neutrophils (activation and chemotaxis of neutrophils).
2. CC chemokines or b-chemokines
(a) Two conserved cysteine residues are located adjacent to each other.
(b) Include MCP-1, eotaxin, MIP-a and RANTES (regulated and normal T cell
expressed and secreted).
(c) Chemotactic for monocytes, eosinophils, basophils and lymphocytes (not
neutrophils).
3. C chemokines or g-chemokines: Lack first and third (two of four) cysteines,
eg, lymphotactin specific for lymphocytes.
4. CX 3 C chemokines: Three amino acid residues between two cysteines, eg, fractalkine.

Q. Write briefly on nitrous oxide (NO).

Ans. NO (also called endothelium-derived relaxing factor) is a soluble gas produced by
endothelial cells (eNOS), macrophages (iNOS) and neurons (nNOS).
• Of these isoforms, eNOS is constitutively expressed (activated rapidly by increase in
calcium).
• iNOS is induced when macrophages are activated by cytokines (TNF, gIFN).
• NO is synthesized from L-arginine by NOS (nitric oxide synthase).
• Acts in a paracrine manner via cyclic GMP.
• Causes vasodilatation, g platelet aggregation, g platelet adhesion, g mast cell-induced
inflammation.
• Regulates leukocyte recruitment and microbicidal activity.

Q. Write briefly on neuropeptides.
Ans. Neuropeptides are small proteins such as substance P and neurokinin A that transmit
pain signals, regulate vessel tone and modulate vascular permeability. They are secreted by
nerve fibres in lungs, GIT and leukocytes.

Q. Write briefly on complement system.
Ans. Complement was first discovered as a heat-labile component of normal plasma
that was found to add to or augment the opsonization of bacteria by antibodies and
facilitate bacterial killing. The name derives from the fact that this system was found to
‘complement’ the antibacterial activity of the antibody.
• Complement system is an important part of the innate and adaptive immune
responses.
• It is constituted by a collection of 30 different proteins which include serum and cell
surface proteins as well as cell membrane receptors.
• The complement proteins, in their precursor zymogen forms, are widely distributed
throughout body fluids and tissues without any adverse effect. They are activated at

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