Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A): Tuberculin and Johnin tests are serological tests employed for diagnosis of Bovine Tuberculosis and Paratuberculosis, respectively.
Reason (R): Both the tuberculin and Johnin tests are based on antigen-antibody complex mediated type 3 hypersensitivity reaction.
In light of the above statements, choose the correct answer from the options given below:

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false and (R) is also false.

Hint:

Remember that mycobacterial skin tests (tuberculin and Johnin) are classic examples of in vivo cellular immunity assays based on Type IV (delayed) hypersensitivity. They do not involve antibodies or serum (serology).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Bovine Tuberculosis (caused by Mycobacterium bovis) and Paratuberculosis or Johne's disease (caused by Mycobacterium avium subsp. paratuberculosis) are chronic mycobacterial diseases.
The classic in vivo diagnostic screening tests for these diseases are the tuberculin and Johnin skin tests, respectively.

Step 2: Detailed Explanation:
Let us analyze both statements:
- Assertion (A): Serological tests are laboratory assays performed on serum to detect circulating antibodies or antigens (such as ELISA or AGID). The tuberculin and Johnin tests are in vivo intradermal skin tests, not serological tests. They are performed by injecting purified protein derivatives (PPD) intradermally into the skin of the neck or caudal fold and measuring the resulting skin thickness. Thus, Assertion (A) is false.
- Reason (R): Type III hypersensitivity is an immune-complex-mediated reaction involving IgG/IgM antibodies and complement deposition (such as the Arthus reaction). The tuberculin and Johnin tests rely on Type IV (delayed-type) hypersensitivity, which is cell-mediated. This reaction is mediated by sensitized T-lymphocytes (specifically Th1 cells) releasing cytokines that recruit macrophages to the injection site over 48 to 72 hours, causing localized swelling and induration. Thus, Reason (R) is false.
Consequently, both the Assertion and the Reason are false.

Step 3: Final Answer:
Both Statement (A) and Statement (R) are false, which corresponds to option (D).