Determine the correctness or otherwise of the following Assertion [a] ...
Assertion [a]: B cells secrete antibodies against a virus while cytotoxic T cells kill virus-infected cells.
Reason [r]: B cells confer active immunity while cytotoxic T cells confer passive immunity.
The correct answer is option 'C' - [a] is true but [r] is false.
Explanation:
B cells and Antibody Production:
- B cells are a type of white blood cell involved in the adaptive immune response.
- When a B cell encounters a virus, it recognizes specific viral antigens on the surface of the virus.
- The B cell then undergoes activation and differentiation into plasma cells, which are specialized cells that secrete antibodies.
- Antibodies are proteins that bind specifically to the viral antigens and neutralize the virus by preventing it from infecting other cells.
- Therefore, it is correct to say that B cells secrete antibodies against a virus.
Cytotoxic T cells and Killing Virus-Infected Cells:
- Cytotoxic T cells, also known as CD8+ T cells, are another type of white blood cell involved in the adaptive immune response.
- Cytotoxic T cells recognize virus-infected cells by recognizing viral antigens presented on the surface of infected cells.
- Once activated, cytotoxic T cells release cytotoxic granules containing enzymes that can kill the infected cells.
- The enzymes induce apoptosis, a programmed cell death, in the virus-infected cells.
- Therefore, it is correct to say that cytotoxic T cells kill virus-infected cells.
Active and Passive Immunity:
- Active immunity refers to the immunity that is developed after exposure to a pathogen or vaccination.
- Active immunity is long-lasting and involves the production of memory B cells and memory T cells that can provide a rapid and specific response upon re-exposure to the pathogen.
- B cells and the production of antibodies are essential for active immunity because they can recognize and neutralize the pathogen.
- Passive immunity, on the other hand, refers to the transfer of pre-formed antibodies or immune cells from one individual to another.
- Passive immunity is temporary and does not involve the production of memory cells.
- Cytotoxic T cells do not confer passive immunity as they are not involved in the transfer of pre-formed antibodies or immune cells.
Conclusion:
Based on the above explanations, it can be concluded that Assertion [a] is true as B cells do secrete antibodies against a virus and cytotoxic T cells do kill virus-infected cells. However, Reason [r] is false as B cells confer active immunity, not passive immunity, and cytotoxic T cells do not confer passive immunity.