Heterophile Antibody & EBV

Heterophile antibodies are antibodies that react with antigens from two or more unrelated species. [1]
Epstein-Barr virus (EBV) is associated with the following diseases:

Infectious mononucleosis (IM) [2, 3]
Burkitt's lymphoma [3]
Nasopharyngeal carcinoma [3]

Heterophile antibodies are clinically significant because they are produced during acute EBV infection (infectious mononucleosis). [1, 4, 5] The presence of these antibodies, along with the classic symptoms of IM (fever, lymphadenopathy, sore throat, and fatigue), can help diagnose the infection. [1] Antibodies to specific EBV antigens, such as VCA, EA-D, and EBNA, are also clinically significant because they can be used to differentiate between current, past, and reactivated EBV infection. [5, 6]
Laboratory methods used to test for heterophile antibodies include:

Monospot test [1, 4]
Mono-diff test [4, 7]
IM immunochromatographic assay [8] Laboratory methods used to test for EBV antibodies include:
IgM and IgG to Epstein Barr viral capsid antigen (VCA) [5]
IgM to the EBV early antigen (EA-D) [5]
Antibody to the EBV nuclear antigen (EBNA) [5]

EBV is transmitted via direct contact with infected saliva. [3]

Rapid Testing for IM

Rapid testing for IM typically involves detecting heterophile antibodies. Here's a description of these tests:

Principle: These tests are based on the principle that heterophile antibodies produced during IM will agglutinate red blood cells from certain animals, like sheep or horse. [4]
Common methodologies and expected results:Monospot test: Patient serum is mixed with sheep red blood cells. Agglutination indicates a presumptive positive result for IM. [4]
Mono-diff test: This test differentiates IM heterophile antibodies from Forssman and serum sickness antibodies by using a series of absorptions with guinea pig kidney cells and bovine stroma. [7] Agglutination patterns with different absorptions indicate the type of heterophile antibody present. [8]
IM immunochromatographic assay: This assay uses a related heterophile antigen bound to colored bovine erythrocyte antigen. If present, the heterophile IM antibody in the patient sample binds to the antigen and travels up a test strip, forming a visible line. [8]
Sensitivity & specificity: Heterophile antibody tests for IM have a sensitivity of around 85-90%, meaning that they detect about 85-90% of true IM cases. [8] The specificity of these tests is generally high, meaning that false positives are relatively uncommon. [4, 7]
Possible technical problems:False-positive results can occur due to the presence of other heterophile antibodies, such as the Forssman antigen or antibodies from serum sickness. [4]
False-negative results can occur in about 10-15% of IM patients, especially early in the course of the infection. [8]

Follow-up Testing for False-Negative Rapid IM

If a rapid IM test is negative but IM is still suspected, follow-up testing can be done using EBV-specific antibody tests. [8] These tests detect antibodies to specific EBV antigens (VCA, EA-D, and EBNA) and can provide a more definitive diagnosis. [5] The expected results for a current EBV infection would be:

Positive anti-VCA IgM and IgG [6]
Positive anti-EA-D IgG [6]
Negative anti-EBNA [6]

Streptococcus pyogenes Virulence and Complications

The M protein of Streptococcus pyogenes contributes to its virulence by:

Adhering to host cells [9]
Resisting phagocytosis [9]
Blocking antibody attachment [10]
Interfering with complement activation [10]

Suppurative complications of streptococcal infections are characterized by pus formation and include:

Pharyngitis ("strep throat") [11]
Pyoderma (impetigo) [11]
Scarlet fever [12]
Toxic shock syndrome [12]
Necrotizing fasciitis [12] Nonsuppurative complications of streptococcal infections are immune-mediated and occur after the initial infection has subsided. They do not involve pus formation and include:
Acute rheumatic fever [12]
Poststreptococcal glomerulonephritis [13]

Rheumatic Fever and Glomerulonephritis

Rheumatic fever is an inflammatory disease that can affect the heart, joints, skin, and brain. It typically develops 1 to 3 weeks after a Streptococcus pyogenes pharyngitis or tonsillitis infection. [12]
Glomerulonephritis is a kidney disease that can cause inflammation and damage to the glomeruli, the tiny filters in the kidneys. It may follow a strep infection of the skin (impetigo) or pharynx (strep throat). [13]

Antibody vs. Antigen Testing for Streptococcal Sequelae

Antibody testing is preferred over antigen testing for the sequelae of streptococcal infections (rheumatic fever and glomerulonephritis) because:

The bacteria are often no longer present in the body by the time these complications develop.
Antibody tests can detect a past exposure to Streptococcus pyogenes, which is a key indicator of these conditions. [14]

ASO Titer and Anti-DNase B Detection

The principle of the antistreptolysin O (ASO) titer is to detect antibodies against streptolysin O, a toxin produced by Streptococcus pyogenes. [15] The test measures the amount of antibody in the patient's serum that can neutralize the toxin. Nephelometric methods are commonly used, measuring the light scatter produced by immune complexes containing streptolysin O antigen and the patient's antibodies. [15]
Causes for false-negative results in an ASO titer include:

Recent antibiotic treatment: Antibiotics can suppress antibody production.
Delayed specimen collection: Antibody levels may not be detectable early in the infection.
Improper specimen handling: Streptolysin O is oxygen-labile, so improper handling can lead to degradation of the antigen and falsely low results.

The presence of anti-DNase B is detected using enzyme immunoassays (EIA) or nephelometric methods. [15] These tests measure the amount of antibody in the patient's serum that binds to DNase B, an enzyme produced by Streptococcus pyogenes.

Streptozyme Test Sensitivity

The Streptozyme test is a slide agglutination test that detects antibodies to five different streptococcal antigens: ASO, anti-hyaluronidase, anti-streptokinase, anti-nicotinamide-adenine dinucleotide, and anti-DNase B. [16] This test has higher sensitivity than individual tests for any single antibody, making it useful for screening for streptococcal antibodies. However, it also has lower specificity than individual tests and can sometimes give false-positive results.