Antigen Antibody Reaction Questions and Answers

Answer: A

Correct answer: antibodies

Agglutination involves particulate antigen - whole cells or coated particles - so very little antibody is needed to produce a visible clumping, and the test detects antibody at concentrations well below what precipitation requires. This is why so many diagnostic serological tests are agglutination tests, and why soluble antigens are deliberately coated onto latex or red cells to convert precipitation into agglutination.

Answer: D

Correct answer: all of these

This is the standard device for gaining sensitivity: adsorb the soluble antigen onto a particle and the reaction becomes an agglutination, visible with far less antibody. Latex beads, bentonite and red cells are all used as carriers, the choice depending on the antigen and on how the result is to be read. The specificity comes from the antigen; the particle only makes the reaction visible.

Answer: A

Correct answer: antibodies to lyse cells via the C8 and C9 components

C8 and C9 are the terminal components: C9 polymerises to form the pore of the membrane attack complex, and the cell lyses osmotically. Complement does also opsonise, through C3b, but the option naming C8 and C9 identifies the lytic function that these particular components perform, which is the one being asked about.

Answer: D

Correct answer: is determined by the heavy chain type

The five heavy chain types - mu, gamma, alpha, delta and epsilon - define IgM, IgG, IgA, IgD and IgE respectively. The light chain, kappa or lambda, is independent of class and is used to describe the antibody’s type rather than its class. Neither the antigen nor the major histocompatibility complex has any part in determining it.

Answer: D

Correct answer: IgA

Secretory IgA is the dominant immunoglobulin in breast milk, as it is in every mucosal secretion. It is a dimer joined by the J chain and carrying the secretory component, which protects it from proteolysis in the infant gut. It is not absorbed but acts within the lumen, coating organisms and preventing their attachment to the mucosa.

Answer: C

Correct answer: IgG

IgG is the only class transported across the placenta, carried actively by the neonatal Fc receptor on trophoblast. This gives the newborn several months of passive protection reflecting the mother’s immune experience. IgM is too large and lacks the receptor interaction, which is why IgM in cord blood indicates the infant’s own response and hence intrauterine infection.

Answer: C

Correct answer: both (a) and (b)

The hybridoma is made by fusing two cells, each supplying what the other lacks. The immunised mouse’s splenic lymphocytes provide the specific antibody but die in culture; the myeloma cells are immortal but make no useful antibody. Fused, the hybrid both secretes the chosen antibody and divides indefinitely, and selective medium kills the unfused partners.

Answer: C

Correct answer: Bind antibodies attached to cell surfaces and to lyse these cells

The classical pathway begins when C1q binds the Fc regions of antibody already attached to a cell surface, and the cascade that follows assembles the membrane attack complex, which perforates the membrane and lyses the cell. Complement also opsonises and generates chemotactic fragments, but lysis of antibody-coated cells is its defining function.

Answer: B

Correct answer: Can reduce the inflammation associated with rheumatoid arthritis

Anti-tumour necrosis factor monoclonals such as infliximab and adalimumab are among the most widely used therapeutic antibodies, and they work precisely because a monoclonal has a single narrow specificity. The other options describe the opposite properties - broad cover, polyclonal origin from immune donors, multiple specificities - which belong to pooled immune globulin.

Answer: D

Correct answer: intestinal tract

The J chain is needed to assemble dimeric IgA and for its transport across the mucosal epithelium, so without it secretory IgA cannot be delivered to the gut lumen. The consequence is repeated intestinal infection, since the mucosal surface loses the antibody that normally prevents organisms from adhering to it.