Question

One characteristic of a B cell is that it: a. has the same structure in both invertebrates and vertebrates. b. recognizes antigens held on class I MHC proteins. c. binds viral infected cells and directly kills them. d. makes many different BCRs on its surface. e. has a BCR on its surface, which is the IgM molecule.

Short answer

The correct answer to the question 'One characteristic of a B cell is that it' is option (e): 'has a BCR on its surface, which is the IgM molecule.'

Step-by-step solution

Analyzing the Characteristics

B cells, also known as B lymphocytes, are a type of white blood cell that plays a significant role in the adaptive immune system by producing antibodies. Each B cell generates a distinct receptor protein (BCR) that is displayed on its cell surface, and the BCR can recognize and bind to a unique antigen. That's why, not all B cells are the same since each recognizes a distinct antigen.

Option Evaluation Step 1

Looking at option (a), it's well known that there are differences in B cells across different species. Hence, this option is incorrect.

Option Evaluation Step 2

Option (b) states that a B cell recognizes antigens held on class I MHC proteins. However, this is a characteristic of T cells, not B cells. So, this option is incorrect.

Option Evaluation Step 3

Option (c) says that B cells bind viral infected cells and directly kill them. This is not correct either. B cells do not directly kill targets, but produce antibodies that can cause death of cells. So, (c) is also incorrect.

Option Evaluation Step 4

Option (d) implies that a single B cell can make many different BCRs on its surface. This is a misconception, as each B cell produces a distinct receptor protein (BCR) that allows it to recognize a different antigen, but a single B cell does not produce multiple different BCRs. Hence, (d) is also incorrect.

Option Evaluation Step 5

Finally, option (e) states that a B cell has a BCR on its surface, which is the IgM molecule. This is correct. IgM is one form of BCR and is expressed on the surface B cells. Thus, (e) correctly describes a characteristic of B cells.