Q.It is often observed that the chances of a person suffering from measles in his or her lifetime are low if he or she has suffered from the disease in their early childhood. Justify the statement.

The key idea is acquired immunity or immunological memory.

When a person suffers from measles in early childhood, their immune system is exposed to the measles virus. This exposure triggers a primary immune response, leading to the production of specific antibodies and specialized memory B and T cells. Upon subsequent exposure to the measles virus, these memory cells rapidly recognize the pathogen and mount a much faster, stronger, and more effective secondary immune response, neutralizing the virus before it …

The statement describes a fundamental principle of adaptive immunity: once the body successfully fights off an infection, it often develops a long-term "memory" of that specific pathogen. This memory allows for a much faster and stronger response if the same pathogen is encountered again, often preventing the disease from developing a second time. This is precisely why childhood diseases like measles, chickenpox, and mumps typically grant lifelong immunity after a single infection.

Here is the justification:

1. First Exposure and Primary Immune Response: When a person, especially a child, is infected with the measles virus for the first time, their immune system mounts a primary immune response. During this phase, specialized white blood cells called B lymphocytes (B cells) and T lymphocytes (T cells) are activated. B cells, with the help of T cells, begin to produce specific antibodies that target and neutralize the measles virus. T cells directly attack infected cells and help coordinate the immune response. This initial response takes time to develop, which is why the person experiences the symptoms of measles.

2. Formation of Memory Cells: As the infection is cleared and the body recovers, most of the activated B and T cells that fought the measles virus die off. However, a crucial subset of these cells differentiates into long-lived memory B cells and memory T cells. These memory cells persist in the body for many years, sometimes even for a lifetime. They are essentially "pre-programmed" to recognize the measles virus.

3. Subsequent Exposure and Secondary Immune Response: If the person is exposed to the measles virus again later in life, these memory cells are rapidly activated. Unlike the primary response, which takes days or weeks to build up, the memory cells can quickly proliferate and differentiate into effector cells (e.g., plasma cells that produce large quantities of antibodies, and cytotoxic T cells that kill infected cells). …