Immunology MCQ - Biotechnology Engineering (BT) MCQ

A normal immune response involves inflammatory response such that antigen is eliminated and host tissues are protected. However, in some conditions this inflammatory response can be harmful to the host. This leads to tissue damage and sometimes death. This inappropriate immune response is termed as hypersensitivity or allergy.

Theantigen leading to allgeric reaction is called an allergen. When immune system first encounters an allergen, it responds by producing IgE class of antibody. IgE, like any other antibody class has a variable region and a constant region. The latter is called Fc region.

Receptors for Fc region are found on many cells of immune system, mast cell is one of them.

The IgE antibody binds to its Fc receptor (FcR) on mast cells. When immune system encounters the same allergen for next time the allgeric reaction follows. It happens because allergen binds to IgE antibody bound with FcR on mast cells. This causes crosslinking of IgE and induces mast cells to undergo degranulation and release their mediators of allergy. These mediator molecules include histamine, heparin, serotonin, prostaglandins etc.

A single antibody molecule is made of two light chains and two heavy chains. These are combined as (one light + one heavy)2. The arrangement is such that a monomeric antibody molecule will have two antigen binding sites. This is true for monomens of all antibody classes viz. IgM, IgG, IgA, IgE and IgD.

The IgM is secreted as a pentameric molecule. Therefore, number of antigen binding sites is 5 × 2 = 10 sites.

However, due to steric hindrance only 5 sites are used for antigen binding.

Also, IgM is the first class of antibody to be produced in an immune response.

Note : Antibody secreting cells are a type of B-cell and called plasma cell.

Antigens are bound to antibody. This is called antigen-antibody interaction. This interaction involves weak

bonds and interaction. These weak bonds and interactions are
• Hydrogen bond
• Ionic interaction
• Hydrophobic interactions

It does not involve covalent bond, a strong bond.
Therefore, correct option is (c).

 Option ( b) - IgG is the right answer. 

( IgG ) is secreted as a monomer that is small in size  allowing it to easily perfuse tissues. It is the only antibody isotype that has receptor to facilitate passage through placenta and provide protection to the fetus in utero. 

Histamines are basic compound and thus have positive charge. Eosin is an acidic dye and thus have negative charge. Thus, interaction between histamine and eosin during staining is electrostatic interaction between positive and negative charges.

Some facts about nitric oxide gas are
• It is an intracellular signalling molecule
• It stimulates guanylyl cyclase to produce cGMP as second messenger
• It is produced by activated neutrophils and macrophages for killing the microbes
• It is produced by deamination of amino acid arginine
Thus, statement (b) is false about nitric oxide gas.

Kupffer cells are named after German anatomist K. Kupffer. These are macrophages and thus phagocytic cells that form part of reticulo-endothelial system.

They act to destroy old RBCs and remove foreign particles from blood flowing through liver.

Therefore, correct option is (b)

Note : Reticulo-endothelial system is a mammalian defence system against foreign bodies.

It consists of macrophage cells located in lymph nodes, liver, spleen and bone marrow.

It is also called mononuclear phagocyte system.

Allelic exclusion is a process that occurs in antibody producing lymphocytes (B-cells) where antibody synthesis is specified by only one in the pair of alleles of the relevant gene.

This is because only one of the alleles is allowed to be active.

Therefore, correct option is (a)

Note : B-cells are diploid. So they will have 2 alleles for a given antibody gene. But only one of them is expressed. This is called allelic exclusion.

The Systemic Acquired Resistance (SAR) is a whole plant resistance response that occurs after an earlier localized exposure to a pathogen. SAR is analogous to innate immune response found in animals.

The activation of SAR needs Salicyclic Acid (SA).

SA activates the signal transduction pathways activating genes involved in SAR. Thus, SA activates SAR after pathogenic attack on one part of plant and induces resistance in other parts. This signal can also move to nearby plants by SA being converted into a volatile ester, methyl salicylate.

Type-II hypersensitivity : In this, IgG class of antibody (Ab) is made against cell surface antigens. This Ab binds to its targets on cell surface. Now, this Ab mediates cell destruction.

The cell destruction is achieved by complement activation or antibody dependent cell mediated cytotoxicity (ADCC). Complement system kills the target cell by inserting its membrane attack complex (MAC) into cell membrane. The pores are formed, cell loses its osmotic balance and dies. MAC is made of proteins.

ADCC involves natural killer cells (NK-cells).

Examples of type-II hypersensitivity reaction are blood transfusion reaction and erythroblastosis foetalis.

So, it involves antibody mediated destruction of cells.

A genetic trait designated nu is controlled by a recessive gene on chromosome 11. Mice homozygous for this trait (nu/nu) are hairless and either lack thymus gland or have a vestigial (non-functional) thymus gland. Such mice are called nude mouse/mice.

Nude mice lack cell-mediated immune response and can not make antibodies to most antigens.

Note :

• SCID mouse are made by deletion of RAG-1 and RAG-2 genes. These genes enzymes responsible for V- (D)-J recombination leading to proper development of T- and B-cells.

These mice lack matured T- and B-cells, hence show servere immunodeficiency similar to human SCID.

These are used in HIV research.

• CBA/N mice have mutation in Bruton’s tyrosine kinase (Btk) gene. It affects their normal B-cell development.

These are used as model of human X-linked immunodeficiency.

• Beige mice arise when bgJ mutation is homozygous i.e. bgJ | bgJ. They show deficiency in NK-cells of immune system. They are used in research of NK-cell deficiency diseases. E.g. Chediak-Higashi syndrome.

In humans and mice, bone marrow is the site of B-cell origin and development. But in birds, a lymphoid organ called bursa of Fabricius is the primary site of B-cell development.

The function of B-cells is to produce antibody on stimulation by an antigen. These antibodies are found in serum and can be quantified.

Since chicken is a bird, removing bursa of Fabricius will impair normal B-cell development. Thus, it will cause low serum level of antibodies.

APCs are macrophages, dendritic cells, B-lymphocytes. These cells behave as professionly APC

MHC I is expressed by all nucleated cells, represent antigen processed by proteosome in cytosol. It presents antigen to be recognized by Tc cells. Antigens that are expressed by MHC I must be 8-10 amino acids long.

Autograft: from one region to another in same person.
Syngraft: between genetically identical persons
Allograft: between genetically different individuals of same species
Xenograft: between individuals of different species.

• CD4:
(i) Expressed by TH cells
(ii) Therefore, TH cells recognize MHC II-Ag complex
• It also acts as a receptor for HIV and has single polypeptide chain in its structure.

Hinge region provides flexibility to variable arms, rich in proline. It is present between CH₁ and CH₂ domains. Only IgA, IgD, IgG classes have hinge region. It plays no role directly to recognize the antigen.

Autoimmunity is a diseased situation when body’s immune system starts to attack and destroy host’s cells and tissues.

Type I diabetes mellitus happens when cells of immune system destroy beta-cells in pancreatic islets of Langerhans.

This leads to drop in insulin production and development of diabetes.

Pernicious anaemia is an autoimmune anaemia. In this, autoantibodies block intrinsic factor, a membrane bound protein on gastric parietal cells. It facilitates absorption of vit. B12. But auto-antibodies block it, so vit. B12 can not be absorbed. Absence of vit. B12 adversely affects proper haematopoiesis and number of functional mature RBCs drops below normal. It leads to anaemia.

While Type II diabetes mellitus and gestational diabetes are related to metabolic imbalances and not autoimmunity.

B-lymphocyte express both membrane bound immunoglobulins like IgM and secreted forms like IgG. These cells directly recognize antigen by membrane bound B-cell receptor  on the IgM. Also behave as an antigen presenting cells.

In the absence of thymus gland, development and function of T-cells are nearly absent. This severely effects  cell mediated immunity. In mice this condition leads to mice having no hair and transparent skin, Such mice are called nude mice and are used in research.

While in humans, such condition leads to severely compromised immune system and is called as DiGeorge`s syndrome.

Apoptosis is characterized by
• decrease in size; plasma mebrane remains intact
• energy dependent, reversible process
• release of cyt-C from mitochondria
• caspases are required for completion of this process