IMMUNOCHEMISTRY MIDTERM

A

What constitutes the body's primary first line of anatomical and physiological defense against invading pathogenic

microorganisms?

A) Skin and intact mucous membranes

B) Complement cascade activation

C) Specific IgG antibody production

D) Cytotoxic T-lymphocyte activation

E) Memory B-cell proliferation

A

Which antibody immunoglobulin class is primarily responsible for toxin neutralization, opsonization, and long-term

secondary humoral immunity?

A) IgG

B) IgE

C) IgA

D) IgD

E) IgM

A

Which cell type acts as the principal effector cell in Antibody-Dependent Cellular Cytotoxicity (ADCC) against large

parasitic organisms?

A) Eosinophils

B) Basophils

C) Plasma cells

D) Erythrocytes

E) Dendritic cells

A

In serologic immunodiffusion testing for Histoplasmosis, what does the presence of an 'M' precipitin band indicate?

A) Active, ongoing, or past exposure/infection

B) Complete absence of fungal exposure

C) Exclusive bacterial co-infection

D) Immediate hypersensitivity allergy only

E) Congenital Rubella Syndrome

A

Despite being obligate intracellular organisms with cell walls, how do Rickettsiae immunologically behave?

A) Gram-negative bacteria

B) Enveloped RNA viruses

C) Encapsulated yeasts

D) Intracellular protozoa

E) Prions

A

Which primary innate cytokine is produced by host cells to directly inhibit viral replication during early infection?

A) Interferon

B) Interleukin-10

C) Erythropoietin

D) Histamine

E) Bradykinin

A

Which pro-inflammatory cytokine acts as the central mediator driving systemic Cytokine Release Syndrome (CRS) in

severe COVID-19?

A) Interleukin-6 (IL-6)

B) Interleukin-4 (IL-4)

C) Interleukin-5 (IL-5)

D) Transforming Growth Factor-beta (TGF-β)

E) Interleukin-10 (IL-10)

A

What hematological finding is recognized as a vital prognostic marker of severe disease and poor outcome in COVID-19

patients?

A) Lymphopenia (decreased lymphocyte count)

B) Eosinophilia (increased eosinophil count)

C) Polycythemia (increased red blood cell count)

D) Basophilia (increased basophil count)

E) Monocytosis (increased monocyte count)

A

What is the gold standard diagnostic method for confirming active SARS-CoV-2 infection by detecting viral nucleic acid?

A) Real-Time Reverse Transcription Polymerase Chain Reaction (RT-PCR)

B) Sabin-Feldman Dye Test

C) Latex Agglutination Test

D) Heterophile Antibody Assay

E) Tzanck Smear Preparation

A

Which organism serves as the definitive host in the complex life cycle of Toxoplasma gondii?

A) Domestic and wild cats (Family Felidae)

B) Anopheles mosquitoes

C) Aedes aegypti mosquitoes

D) Freshwater snails

E) Ixodes ticks

B

Which antibody class is produced first in significant quantities following a host's primary exposure to an infectious

pathogen?

A) IgA

B) IgM

C) IgE

D) IgD

E) IgG4

B

What complement fixation (CF) antibody titer for Blastomycosis is considered clinically diagnostic of active fungal

infection?

A) 1:2

B) ≥ 1:32

C) 1:4

D) 1:1

E) Less than 1:2

B

Mycoplasma species lack a peptidoglycan cell wall. Immunologically, how do these organisms behave during infection?

A) Like helminths

B) Like bacteria

C) Like DNA viruses

D) Like spirochetes

E) Like systemic yeasts

B

Which Major Histocompatibility Complex (MHC) molecule presents intracellular viral peptide antigens to CD8+ Cytotoxic

T lymphocytes?

A) MHC Class II

B) MHC Class I

C) MHC Class III

D) CD1a

E) Factor H

B

Which coagulation parameter serves as the single most important marker for predicting thrombosis, DIC, and mortality

in severe COVID-19?

A) Serum Albumin

B) D-dimer

C) Hemoglobin

D) Blood Urea Nitrogen

E) Hematocrit

B

Which mosquito vector is primarily responsible for transmitting Dengue virus between human hosts in urban endemic

areas?

A) Anopheles minimus

B) Aedes aegypti

C) Culex quinquefasciatus

D) Mansonia uniformis

E) Phlebotomus papatas

B

What rapidly multiplying asexual form of Toxoplasma gondii causes acute tissue destruction and cellular invasion?

A) Bradyzoite

B) Tachyzoite

C) Arthrospore

D) Sporozoite

E) Amastigote

B

Rubella virus is an enveloped, single-stranded RNA virus belonging to which viral family?

A) Paramyxoviridae

B) Matonaviridae

C) Coronaviridae

D) Flaviviridae

E) Retroviridae

B

Group A Streptococcus (*Streptococcus pyogenes*) adheres to human epithelial cells using which membrane

component?

A) Erythrogenic toxin

B) Lipoteichoic acid

C) Streptolysin S

D) Hyaluronidase

E) C-carbohydrate

B

What classic primary mucosal/cutaneous lesion develops at the site of bacterial entry in Primary Syphilis?

A) Condyloma lata

B) Hard, painless chancre

C) Erythema migrans

D) Vesicular cold sore

E) Rose spot papule

C

What is the primary functional role of IgE antibodies during an infection caused by parasitic helminths?

A) Direct bacterial cell wall lysis

B) Neutralization of viral attachment proteins

C) Mediating hypersensitivity responses and binding mast cells/eosinophils

D) Transport of secretory IgA across membranes

E) Inhibition of cytotoxic T cells

C

What is the common clinical name for Coccidioidomycosis, caused by inhaling soil-dwelling Coccidioides immitis

arthrospores?

A) Rose gardener's disease

B) Chicago disease

C) Valley Fever (or Desert / San Joaquin Fever)

D) Breakbone fever

E) Lockjaw

C

Sporotrichosis, caused by traumatic cutaneous inoculation of Sporothrix schenckii via thorns, is known by which

eponym?

A) Woolsorter's disease

B) Undulant fever

C) Rose gardener's disease

D) Rabbit fever

E) Black death

C

What diagnostic latex agglutination titer in CSF or serum confirms an active Cryptococcus neoformans infection?

A) Titer less than 1:2

B) Absence of antigen

C) Latex agglutination titer ≥ 1:4

D) Positive ASO antibody titer

E) Elevated D-dimer

C

Which immune effector population represents the MOST critical host defense mechanism for clearing viral infections?

A) Eosinophils

B) Neutrophils

C) T cells (T lymphocytes)

D) Basophils

E) Erythrocytes

C

In the clinical progression of Dengue fever, during which phase does plasma leakage, shock, and severe hemorrhage

occur?

A) Febrile Phase

B) Incubation Phase

C) Critical Phase (Defervescence)

D) Recovery Phase

E) Prodromal Phas

C

What classic historical reference assay uses complement-mediated parasite lysis to measure anti-*Toxoplasma* IgG

antibodies?

A) Western Blot

B) Rapid Plasma Reagin (RPR)

C) Sabin-Feldman Dye Test

D) VDRL Test

E) Weil-Felix Test

C

Congenital Rubella Syndrome (CRS) carries the highest risk of severe teratogenic defects when maternal infection

occurs during which period?

A) Third trimester

B) Intrapartum period

C) First trimester of pregnancy

D) Postpartum period

E) Late second trimester

C

Which major surface protein of Group A Streptococcus inhibits host phagocytosis and possesses over 60 distinct

serotypes?

A) Erythrogenic toxin

B) Streptolysin S

C) M protein

D) Hyaluronidase

E) Lipoteichoic acid

C

Which nonsuppurative complication of Group A Streptococcus occurs EXCLUSIVELY following pharyngeal infections

and NOT skin infections?

A) Poststreptococcal glomerulonephritis

B) Impetigo

C) Acute Rheumatic Fever (ARF)

D) Erysipelas

E) Scarlet fever

D

Which immunodiffusion serologic marker in Histoplasmosis specifically indicates an active, ongoing fungal infection?

A) C band

B) A band

C) P band

D) H band

E) M band

D

Detection of which fungal cell wall antigen in serum via EIA is used to diagnose invasive Aspergillosis?

A) Cryptococcal glucuronoxylomannan

B) Histoplasmin M

C) Streptolysin O

D) Aspergillus galactomannan antigen

E) C-reactive protein

D

Which Major Histocompatibility Complex (MHC) class presents exogenous extracellular antigens to CD4+ Helper T

cells?

A) MHC Class I

B) MHC Class III

C) CD1d

D) MHC Class II

E) Factor B

D

In COVID-19 clinical chemistry, elevated serum levels of which enzyme serve as a classic marker of systemic tissue

damage?

A) Amylase

B) Lipase

C) Alkaline Phosphatase

D) Lactate Dehydrogenase (LDH)

E) Acid Phosphatase

D

What encysted, slow-growing stage of Toxoplasma gondii persists chronically in host neural and muscular tissues?

A) Tachyzoite

B) Oocyst

C) Promastigote

D) Tissue cyst (containing Bradyzoites)

E) Cercaria

D

Subacute Sclerosing Panencephalitis (SSPE) is a fatal, late neurological complication caused by persistent infection

with which virus?

A) Rubella virus

B) Varicella-Zoster Virus

C) Cytomegalovirus

D) Rubeola (Measles) virus

E) Herpes Simplex Virus Type 1

D

What diagnostic microscopic cytopathic feature ('owl's eye' intranuclear inclusions) is characteristic of Cytomegalovirus

(CMV)?

A) Negri bodies

B) Guarnieri bodies

C) Cowdry A bodies

D) 'Owl's eye' intranuclear inclusion bodies

E) Councilman bodies

D

Primary infection with Varicella-Zoster Virus (VZV) causes chickenpox. What condition results from reactivation of

latent VZV?

A) Roseola infantum

B) Erythema infectiosum

C) Infectious mononucleosis

D) Shingles (Herpes Zoster)

E) Scarlet fever

D

Which oxygen-labile, antigenic extracellular toxin of Group A Streptococcus lyses RBCs by binding membrane sterols?

A) Streptolysin S

B) Hyaluronidase

C) Erythrogenic toxin

D) Streptolysin O (SLO)

E) Streptokinase

D

What diagnostic microscopic method allows direct visualization of live, motile Treponema pallidum spirochetes from

primary lesions?

A) Gram stain

B) Acid-fast stain

C) Calcofluor white stain

D) Darkfield microscopy

E) Wright-Giemsa stain

E

Which oxygen-stable, non-antigenic extracellular toxin produced by Streptococcus pyogenes causes beta-hemolysis

on blood agar?

A) Streptolysin O

B) Hyaluronidase

C) M protein

D) Streptokinase

E) Streptolysin S

E

Which extracellular enzyme produced by Group A Streptococcus acts as a 'spreading factor' by degrading connective

tissue ground substance?

A) Streptolysin O

B) DNase B

C) Streptokinase

D) Erythrogenic toxin

E) Hyaluronidase

E

Which toxin produced by lysogenized Group A Streptococci causes the characteristic diffuse erythematous rash of

Scarlet Fever?

A) Streptolysin S

B) Alpha toxin

C) Lipid A endotoxin

D) Enterotoxin B

E) Erythrogenic toxin (Pyrogenic exotoxin)

E

To prevent early-onset Group B Streptococcal (GBS) sepsis in neonates, pregnant mothers undergo routine screening at

how many weeks?

A) 10–12 weeks

B) 16–20 weeks

C) 24–28 weeks

D) 28–32 weeks

E) 35–37 weeks gestation

E

Secondary Syphilis is characterized by systemic dissemination. What classic dermatologic finding is present in 80% of

cases?

A) Gummatous ulcers

B) Tabes dorsalis lesions

C) Aortic ring dilation

D) Solitary painless chancre

E) Generalized maculopapular rash including palms and soles

E

What flat, moist, highly contagious papular skin lesion develops in moist intertriginous areas during Secondary Syphilis?

A) Hard chancre

B) Subcutaneous gumma

C) Shingles bulla

D) Herpetic cold sore

E) Condyloma lata

E

In Histoplasmosis serology, what complement fixation or immunodiffusion titer is diagnostic of active infection?

A) 1:2

B) 1:4

C) 1:8

D) 1:16

E) ≥ 1:32

E

To prevent transfusion-transmitted Cytomegalovirus (CMV) in high-risk immunocompromised recipients, which

procedure is used?

A) Simple saline washing

B) Thermal inactivation at 56°C

C) Acid wash buffer

D) Room temperature incubation

E) Leukoreduction (white blood cell filtration)

E

What characteristic microscopic finding on a Tzanck smear from vesicular fluid scrapings confirms a herpesvirus

infection (HSV or VZV)?

A) Gram-negative diplococci

B) Encapsulated budding yeasts

C) Acid-fast bacilli

D) Asteroid bodies

E) Multinucleated giant cells with intranuclear inclusions

E

What liver-derived acute-phase protein stimulated by IL-6 serves as a key circulating marker reflecting inflammation in

COVID-19?

A) Myoglobin

B) Calcitonin

C) Haptoglobin

D) Transferrin

E) C-reactive protein (CRP)