MLT GlobeSCFHS exam preparation (Saudi Arabia) – page 11
749 practice MCQs for the SCFHS medical laboratory exam. Level: Intermediate.
The first immunoglobulin chain produced by a developing pre-B cell, found in the cytoplasm, is the:
Heavy-chain genes rearrange first; cytoplasmic μ chain pairs with a surrogate light chain as the pre-B-cell receptor. Light chains rearrange afterwards.
In a lymph node, T lymphocytes are found mainly in the:
The paracortex (deep cortex) is the T-cell zone, where dendritic cells present antigen. Follicles and germinal centres are B-cell areas.
In the spleen, the periarteriolar lymphoid sheath (PALS) of the white pulp contains mainly:
The PALS surrounding central arterioles is the splenic T-cell zone; B-cell follicles lie next to it. Red cell removal takes place in the red pulp.
Which cell type normally lacks MHC class I molecules?
MHC class I is expressed on almost all nucleated cells and platelets; mature red cells have lost their nucleus and have essentially no class I. Hepatocytes, neutrophils and B cells all express it.
Rheumatic heart disease after group A streptococcal pharyngitis arises because antibodies to streptococcal M protein also bind cardiac tissue. This mechanism is called:
In molecular mimicry, a microbial antigen resembles a self antigen, so the immune response cross-reacts with host tissue. Immune privilege describes sites where immune responses are limited.
The measles–mumps–rubella (MMR) vaccine is an example of a:
MMR contains weakened live viruses that replicate briefly and give strong, long-lasting immunity. Toxoid vaccines contain inactivated bacterial toxins, as in tetanus.
The tetanus vaccine contains:
Tetanus disease is caused by toxin, so the vaccine uses an inactivated toxin (toxoid) that induces neutralising antibody. There is no live tetanus vaccine.
Which type of bond is NOT involved in antigen–antibody binding?
Antigen–antibody binding uses only weak non-covalent forces, which is why the reaction is reversible. Hydrogen, ionic, van der Waals and hydrophobic interactions all contribute.
The overall binding strength between a multivalent antibody and a multivalent antigen, combining all binding sites, is called:
Avidity is the combined strength of many binding sites, so IgM can bind strongly even with low-affinity sites. Affinity is the strength of one binding site with one epitope.
The antigen in the RPR card test consists of:
RPR uses a cardiolipin-lecithin-cholesterol (reagin) antigen bound to charcoal so flocculation is visible without a microscope. Recombinant treponemal proteins are used in treponemal immunoassays.
A lateral-flow (immunochromatographic) test shows a coloured test line but no control line. The correct interpretation is:
The control line confirms that the sample flowed correctly and reagents worked. Without it, any result is invalid regardless of the test line.
In the Widal test for enteric fever, the 'H' antigen refers to the:
In the Widal test, O is the somatic lipopolysaccharide antigen and H is the flagellar protein antigen. The Vi capsular antigen is used separately, mainly to detect carriers.
A kidney recipient develops rising creatinine 3 weeks after transplant. Biopsy shows T lymphocytes infiltrating the tubules. The most likely process is:
Acute cellular rejection occurs days to months after transplant and is mediated by recipient T cells attacking donor tissue, seen as tubulitis. Hyperacute rejection occurs within minutes from preformed antibodies.
Years after a heart transplant, a patient shows gradual graft failure with concentric intimal thickening of graft arteries. This is:
Chronic rejection develops over months to years, with vascular intimal fibrosis (graft vasculopathy) and progressive loss of function. Hyperacute rejection happens within minutes of reperfusion.
Which loci code for HLA class II molecules?
Class II molecules are encoded by the DR, DQ and DP loci and are expressed on antigen-presenting cells. HLA-A, -B and -C are class I; complement genes are in the class III region.
Why must donor and recipient be ABO compatible for kidney transplantation?
Graft endothelium carries A and B antigens, so recipient anti-A or anti-B can cause hyperacute antibody-mediated rejection. ABO and HLA are separate systems.
A child with partial albinism and recurrent pyogenic infections has giant cytoplasmic granules in neutrophils on the blood film. The diagnosis is:
Chédiak-Higashi syndrome (LYST mutation) shows giant lysosomal granules, partial albinism and poor phagocyte killing. Chronic granulomatous disease has normal granule morphology.
Botulinum toxin causes flaccid paralysis by:
Botulinum neurotoxin cleaves SNARE proteins so acetylcholine cannot be released at the neuromuscular junction, causing descending flaccid paralysis.
Obligate anaerobes are damaged by oxygen mainly because they lack:
Without superoxide dismutase and catalase, obligate anaerobes cannot remove superoxide and hydrogen peroxide formed when oxygen is present, so these toxic products damage them.
When a broth microdilution panel is inoculated, a small amount of the inoculum is also streaked onto a blood agar plate. The main purpose of this 'purity plate' is to:
The purity plate shows whether the inoculum was a pure culture; a mixed culture gives unreliable MICs. The growth control well checks viability, not purity.