Study Guide Questions For Immunology

(1) Name the two types of parasites based on cellular localization

Ans: Intracellular parasites and extracellular parasites.

(2) Explain the role of neutrophils in innate immunity

Ans: Neutrophils particularly polymorphonuclear neutrophils (PMNs) are part of the surveillance system in the body fluids where they can identify any invading pathogen, attack/engulf them and destroy it.

(3) The membrane attack complex is formed by proteins

Ans: Complement system proteins especially C5b, C6, C7, C8α C8β and C9.

(4) Anaphylatoxins are

Ans: The peptide fragments C3a and C5a of the complement system protein C3 and C5 respectively. They have an antimicrobial property and induce other cells to release cytokines. C5a especially produces chemotaxis for macrophages, neutrophils, basophils and activated B and T cells. These are also involved in vasodilation and enhancing the permeability of blood vessels.

(5) What are defensins

Ans:
These are, positively charged, cysteine-rich, antimicrobial peptides produced in epithelial cells and granulocytes in response to invading pathogens upon stimulation by chemokines such as IL-1 and TNF-α.

(6) Ligands for Toll Like receptor 3(TLR3) are

Ans: dsRNA (double-stranded RNA) from viral infections

(7) Name one chemokine. Explain the role of chemokines

Ans:
Interleukin-6 is a chemokine. Chemokines are signaling molecules secreted from immune cells such as lymphocytes and leucocytes and cause chemotaxis as well as regulation of gene expression in their target cells during inflammation and defense.

(8) Describe the interferon response

Ans:
Interferons are a family of glycoproteins released during viral infections or other clinical immune responses and are one of the important mediators of the first line of defense in innate immunity. These are cytokines that are involved in immunity against viruses, cancers, and other immunomodulatory actions. As soon as there is any viral infection, interferons are released and then through various mechanisms, they lead to the expression of Interferon responsive genes (IRI), a few of them (say OAS members) may lead to activation of certain nucleases (say RNASEL) that cleave the RNAs of invading viruses and pathogens. This causes inhibition of protein synthesis and thus a breakdown of viral or pathogen replication.

(9) B-cells recognize antigen by
Ans: B- cell receptor (BCR)

and T-cells recognize antigen by

Ans: T – cell receptor (TCR).

(10) MHC class 1 process and present antigens of

Ans: endogenous parasites and MHC class 2 present antigens of
Ans: exogenous.

(11) Describe the role of RAG1 and RAG2 in recombination

Ans:
RAG1 and RAG2 are recombination activating genes expressed in lymphocytes. They are involved in VDJ recombination. The coding sequences of Immuno-globulin and TCR genes are flanked by recombination signal sequences (RSS) which are recognized by a protein complex formed by RAG1 and RAG2. These DNA sequences are cleaved at the point between RSS and the coding sequences, following which the nascent broken ends join and gene rearrangement thus occurs.

(12) Describe how MHC class 1 antigens are processed

Ans:
Class I MHC antigens are processed via an endogenous pathway. Endogenous antigens are first degraded by the proteasome. Then they have assembled with MHC class I receptors at Rough Endoplasmic Reticulum lumen. Then through the Golgi apparatus, they are transported to be presented on the cell membrane of the Antigen-presenting cells.
Class 1 MHC antigen through the antigen-presenting cells interact with the cytotoxic or CD8+ T cells. In a naïve T cell, they are not phagocytosed automatically. A costimulatory signal is required from CD28 and CD80/86 along with paracrine cytokine signaling such as IL-12 and autocrine signaling with IL-2. Thus the T cell is activated. This follows intracellular signaling through which molecules such as perforins and granzyme are produced that kill the target cells.

(13) Describe the function of transporter associated with antigen processing (TAP)

Ans: TAP are the hetero-dimeric proteins situated on the surface of the rough endoplasmic reticulum(RER), that mediate the transfer of peptides generated from antigen degradation by the proteasome, to the inside of the lumen of RER. In the RER these peptides bind with class I MHC.

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