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Infectious Mononucleosis (IM) Overview

  • Definition: Infectious Mononucleosis (IM) is a viral infection often caused by the Epstein-Barr virus (EBV).

Causative Agent

  • Virus Involved: Epstein-Barr Virus (EBV)

  • Mode of Transmission:

    • Infectious mono transmission occurs via oral contact with infected saliva, often referred to as the "kissing disease."

  • Infection Sites:

    • The virus primarily infects epithelial cells in the oropharynx and B-cells in the immune system.

Symptoms of Infectious Mono

  • Symptoms can vary significantly based on the age of the infected individual:

    • Adolescents and Adults:

    • Presentation includes fever, swollen lymph nodes (lymphadenopathy), and sore throat.

    • Children and Elderly:

    • May be asymptomatic or present with mild symptoms.

Laboratory Diagnosis of Infectious Mono

  • Key Laboratory Findings:

    • Presence of atypical reactive lymphocytes

    • Detection of heterophile antibodies

    • Increased percentage of lymphocytes in the blood (approximately 60-70% relative abundance).

Heterophile Antibodies

  • Definition:

    • Heterophile antibodies are early antibodies detectable typically within 1 week to 3 months after infection.

    • These antibodies possess the capability to react with red blood cells from unrelated species, including those from horses, sheep, and cows.

  • Understanding Heterophile Antibody:

    • An antibody that reacts with an antigen from a different species (plant or animal), which differentiates it from the original antigen that caused the immune response.

Immune Response to EBV

  • Evasion Strategy by EBV:

    • EBV can evade the host immune response by reducing the expression of Major Histocompatibility Complex I (MHC I) in infected cells.

    • This reduction hinders the recognition of infected cells by cytotoxic T lymphocytes (CTLs).

Immunosorbent Assay for Infectious Mono

  • Test Description:

    • The assay uses known antigens from bovine red blood cells (RBCs).

    • The test looks for the presence of heterophile antibodies (Isotype IgM) in the patient's serum, indicating recent infection with EBV.

  • Detection Timing:

    • Heterophile antibodies are typically detectable early in the course of EBV infection.

Test Principle and Procedure

  • Principle of the Test:

    • Bovine RBCs, bound to a blue color conjugate, are present in the test dip region.

    • Heterophile antibodies in patient serum bind to bovine RBCs forming a complex in the dip region.

    • The unbound complex travels up the dipstick to the test region, where heterophile antibodies bind to the immobilized bovine RBCs, resulting in a colored line.

Step-by-Step Protocol:

  1. Add 1 drop of the positive control (blue cap).

  2. Add 1 drop of the diluent.

  3. Mix the solution thoroughly.

  4. Insert the dipstick into the tube with the arrows pointing downward and wait for 5 minutes.

  5. Read the results as instructed.

Interpretation of Results

  • Positive Result:

    • Displays two lines: a blue line in the test region and a red line in the control region.

  • Negative Result:

    • Exhibits one red line present only in the control region.

  • Invalid Result:

    • No lines appear or the viewing window looks cloudy, indicating an issue with the test.

Important Notes

  • Disclaimer Regarding Results:

    • Positive result lines may be very faint, requiring careful reading and interpretation.

Review Questions

  • What is the causative agent of infectious mononucleosis?

  • Which cells are infected by this agent?

  • Are symptoms consistent across all age groups?

  • What distinguishes heterophile antibodies in this context?

  • What is known and unknown in the context of this assay?

  • How does a positive result appear versus a negative result?