INF-alphaINF-alpha inhibits viral replication, increase lytic potential of NK cells, increase MHC class I expression and stimulate the development of TH 1 cells.

IgA is a dimer where 2 four-chain units are held together by the J chain through disulfide bridges. Each four chain unit has 2(paratopes) antigen binding sites. Thus 2 four chain unit is capable of binding 4 Ag molecules.

 Di George syndrome: In Di George syndrome, thymus embryogenesis is defective and few T cells develop resulting in severely compromised humoral as well as cellular immunity.

Acetylcholine receptor. In myasthenia gravis auto antibody binds to the acetylcholine receptors on the motor end plate of the muscle blocking the normal binding of acetylcholine also induced compliment mediated lysis of cells.

Specific epitope : monoclonal antibody has a single binding site for specific portion of a macromolecular antigen called epitope, whereas polyclonal antibodies have heterogeneous collection of binding sites for different epitope.

Activated B cell. Class switching is a process by which the isotype of the Abs produced in response to an Ag change as the humoral response proceeds. Different cytokine is induced switching to different antibody classes, enabling the immune system to respond in the most effective ways to different types of microbe. Activated (mature) B cell IgM+ IgD undergoes class switching by induced recombination of switch (S) region such that the VDJ primary RNA is spliced onto the RNA from the downstream C gene, producing a heavy chain with a new constant region and therefore a new class of Ig.

Only when loaded on to MHCT,  cell use TCR to recognize peptide Ag displayed by MHC on antigen presenting .cells.

Initiates classical pathway C1q binds to Fc portion of AB. C1r and C1s are proteases that lead to C4 and C2 activation.

Type IV delayed hypersensitivity. The tuberculin skin test (TST) is an example of type IV hypersensitivity. The test is done by injecting small amount of tuberculin purified protein derivative (PPD) under the top layer of skin. The response in Mycobacterium tuberculosis exposed individual begins within 8 hours  and a reddened area surrounds the injection site becomes indurate (firm and hard) within 12-24 hrs.  The TH1 cell that migrates to the injection site is responsible for the indurations.

C3bBb. The microbe-bounded C3b becomes substrate for the binding of another protein called Factor B, which is broken down by a plasma membrane to generate the Bb fragment. This fragment remain attached to C3b and the resulting C3bBb acts as C3 convertase in alternative pathway.

Both P and Q are true. In this procedure, myeoloma cells are engineered to be deficient enzyme HGPRT. After fusion of lymphocytes with HGPRT negative myeloma cells, aminopterin containing medium, supplemented with hypoxanthine and thymidine to ensure as adequate substrate supply for salvage pathway (HAT medium) is added, which kills myeloma cells but allows hybridomas to survive as they inherit HGPRT from lymphocyte parent.

Avidity when the Ag consists of many epitopes (here 4) are mixed with Ab (here IgG) having multiple (here 2) binding sites, the interaction of such type between multivalent Ab and Ag is called, the Avidity.

Eosinophil is a phagocytic cell important in the body’s defense against parasitic organism. Kuffer cell is one type of tissue macrophages found in liver.  Dendritic cell is an antigen presenting cell that is not phagocytic.  Mast cell is associated with type I hypersensitivity.  Degranulation of mast cell occur in type I hypersensitivity.

Vaccine induces the active immunity in human body.

Aminopterin is used to select hybridoma over myeloma . Aminoptorine inhibits the denovo nucleotide synthesis pathway . However normal cells survive in a medium as they are able to use salvage pathway for nucleic acid biosynthesis. But if the cell unable to produce the enzyme Hypoxanthine Guanine Phospho Ribosyl –Transferase ( HGPRT ) utilized in salvage pathway, they die. Here in this method, myeoloma cell lack that particular enzyme thus, they die in Aminopterin containing medium.

Purified antigen vaccine. Toxoid is one type purified antigen vaccine and composed of molecules purified directly from the pathogen. Chemically modified exotoxin retaining antigenicity without toxicity is known as toxoid.

Option  2 is correct due to P-5, Q-1, R-2 and S-3 are correctly  matched.

Properdine stabilizes the C3 convertase on microbial surface.

4Ag/IgG = 2 : 1Ag = 2 IgG. Since, one IgG binds two epitopes.Ag = 2 (2 epitopes)Ag = 4 Epitopes.

Immunize the mother with toxoid late in pregnancy. The Tetanus toxoid (TT) vaccine is given to mother as well as neonates. Ab s formed in mother’s body after vaccination, are passed on to neonate who have acquired passive immunity.