B cells and humoral immunity

Question 1

Question: What is the initial phase of the specific response to infection, and what occurs during this phase regarding T cells?

Answer 1

Answer: The first phase of the specific response to infection involves the cloning of the relevant T cells to increase their numbers. During this phase, T cells proliferate through mitosis to generate a larger population of T cells with specific T cell receptors (TCRs) capable of recognizing the antigens presented by infected cells.

Question 2

Question: How do some T cells contribute to the subsequent phase of the immune response?

Answer 2

Answer: Some of the T cells produced during the initial phase of the immune response secrete factors, such as cytokines, that stimulate B cells to divide and undergo proliferation.

Question 3

Question: What role do B cells play in the next phase of the specific immune response?

Answer 3

Answer: In the next phase of the specific immune response, known as humoral immunity, B cells are actively involved. Upon stimulation by factors secreted by T cells, B cells proliferate and differentiate into plasma cells, which are responsible for producing antibodies specific to the antigens presented by the pathogen. These antibodies play a crucial role in neutralizing pathogens and marking them for destruction by other components of the immune system.

Question 4

Question: Where are B cells formed, and what is the process they undergo before being released into the bloodstream?

Answer 4

Answer: B cells are formed from stem cells in the bone marrow. They remain in the bone marrow to mature before being released into the bloodstream after birth.

Question 5

Question: How do B cells contribute to the immune response?

Answer 5

Answer: B cells play a crucial role in the immune response by producing antibodies that specifically recognize and bind to antigens. These antibodies facilitate the neutralization and elimination of pathogens, such as viruses and bacteria, and mark them for destruction by other immune cells.

Question 6

Question: What is the diversity of B cells, and what accounts for this diversity?

Answer 6

Answer: There are millions of different B cells, each producing a unique antibody that responds to a specific antigen. This diversity arises from the genetic rearrangement of B cell receptor genes during B cell development in the bone marrow. As a result, B cells can recognize and respond to a wide range of antigens encountered during infections or immunizations.

Question 7

Question: Define antigen, and provide an example.

Answer 7

Answer: An antigen is a molecule that can produce an immune response in the body. For example, a protein on the surface of a pathogen cell, such as a virus or bacterium, can serve as an antigen, triggering the immune system to mount a defense against the invading pathogen.

Question 8

Question: Describe the process of humoral immunity when a pathogen or its toxins enter the bloodstream.

Answer 8

Answer:
When a pathogen or its toxins enter the bloodstream, they encounter numerous B cells. Among these B cells, a few will carry the appropriate antibody molecule, also known as immunoglobulin or Ig, on their surface membrane. These B cells will attach to antigens on the surface of the pathogen or toxin.

Question 9

Question: What occurs during the process of humoral immunity when B cells encounter antigens in the presence of signals from T helper cells?

Answer 9

Answer:
Given the appropriate signals from T helper cells, the B cell undergoes rapid division, resulting in the production of large numbers of genetically identical daughter cells, or clones.

Question 10

Question: What happens to some of the daughter cells produced during B cell division in humoral immunity?

Answer 10

Answer:
Some of the daughter cells develop into plasma cells, which are specialized cells that produce and secrete large quantities of their specific antibody. Plasma cells can secrete up to 2000 molecules of their specific antibody per second.

Question 11

Question: What is the role of memory cells in humoral immunity?

Answer 11

Answer:
Some daughter cells generated during B cell division develop into memory cells. These memory cells circulate in the bloodstream without actively secreting antibodies. However, they retain the ability to recognize the specific antigen encountered during the initial infection. In the event of a second exposure to the same pathogen, memory cells can rapidly mount an enhanced immune response, leading to quicker and more effective clearance of the pathogen.

Question 12

Question: What characterizes the primary immune response in the context of antibody production by plasma cells?

Answer 12

Answer:
During the primary immune response, plasma cells are responsible for secreting antibodies directly. These antibodies target and destroy the pathogen as well as any toxins it produces. Plasma cells, although short-lived, are highly efficient, producing around 2000 antibodies every second. This immediate response by plasma cells constitutes the primary immune response against the infection.

Question 12

Question: What role do memory B cells play during the primary immune response?

Answer 12

Answer:
During the primary immune response, memory B cells are also produced alongside plasma cells. Memory B cells have the unique ability to survive for decades, circulating in the blood and tissue fluid. While they do not actively secrete antibodies during the primary response, memory B cells play a crucial role in providing long-term immunity. In the event of a subsequent exposure to the same pathogen, memory B cells quickly mount a secondary immune response, leading to a faster and more robust defense against the infection.

Question 13

Question: What characterizes the primary immune response in terms of antibody production by plasma cells?

Answer 13

Answer: During the primary immune response, plasma cells secrete antibodies directly. These antibodies target and destroy the pathogen as well as any toxins it produces. Plasma cells, although short-lived, are highly efficient, producing around 2000 antibodies every second. This immediate response by plasma cells constitutes the primary immune response against the infection.

Question 14

Question: What are the characteristics of the secondary immune response?

Answer 14

Answer:

A much smaller amount of antigen induces an immune response because memory cells are already present.
The response is much more rapid, and much more antibody is produced.
The speed of the secondary response is such that the pathogen may be destroyed before infection takes hold, and the symptoms may be only mild or even absent.
Memory cells provide long-term immunity against the original infection; it is known as the secondary immune response.

Question 14

Question: Why do some diseases like chickenpox and measles typically occur only once in a person’s lifetime?

Answer 14

Answer: Diseases like chickenpox and measles typically occur only once in a person’s lifetime because the pathogens that cause them are of a single type. Once the immune system has encountered and developed immunity to these pathogens, subsequent infections are rare.

Question 15

Question: How does antigenic variability contribute to the recurring nature of infections like influenza?

Answer 15

Answer: Antigenic variability, such as in influenza viruses, leads to the presence of multiple strains with constantly changing antigens. As a result, each infection with a different strain of the influenza virus may be perceived as a “primary infection” by the immune system, even if the individual has been previously infected with a different strain. This variability allows the virus to evade the immune response and causes recurring infections over time.

Question 16

Question: What distinguishes diseases like influenza from others like chickenpox and measles in terms of antigenic variability?

Answer 16

Answer: Diseases like influenza exhibit high levels of antigenic variability, with over 100 different strains and constantly changing antigens. In contrast, diseases like chickenpox and measles are caused by pathogens of a single type, resulting in less variability in antigens and typically only one infection during a person’s lifetime.