How are memory cells different from plasma cells? (A) Memory cells remain in the circulation for a longer time period. (B) Memory cells have only one type of antibody receptor on their cell surface, whereas plasma cells have many different types of antibody receptors. (C) Memory cells are no longer able to multiply and differentiate. (D) Memory cells have a higher rate of protein synthesis. Or (E) memory cells are able to respond to a wider range of antigens.
Before we answer this question, we first need to discuss what memory cells and plasma cells are. Both cell types are part of the humoral immune response, even though memory cell is a broad term and these cells can also be part of the cell-mediated immune response. The humoral immune response starts to function when naïve B cells find an antigen with their B cell receptors, which are also called BCR or antibody receptors. This binding can lead to the activation and proliferation of a B cell.
This activated B cell can then further proliferate and differentiate to become either a plasma cell or a memory B cell. A plasma cell is highly differentiated, short-lived, and produces a lot of proteins called antibodies, which will help fight an infection. A memory cell will remain in the immune system for a long time. If the body encounters the same antigen, the memory cells will remember this antigen as they carry the corresponding B cell receptor on their surface. This helps the immune system to react to a recurring infection much faster than it did to the first occurrence.
Now, let’s have a look at our answer choices. We know that memory cells are able to multiply and differentiate, as that’s what they’ll do when the body is infected a second time with a pathogen carrying the same antigen. We can therefore eliminate option (C). As memory cells and plasma cells derived from the same activated B cell, they produce the same antigen binding protein and will therefore bind to the same antigen. Knowing this, we can exclude answer choice (E).
With this knowledge, we can further deduce that memory B cells do indeed have only one type of antibody receptor on their cell surface and that plasma cells do not have many different types of antibody receptors. This means we can eliminate option (B), as it claims that plasma cells have many different types of antibody receptors, which is not true. It’s the function of a plasma cell to release a lot of antibodies. Plasma cells therefore have a much higher rate of protein synthesis than memory cells. So answer choice (D) can be excluded too.
The key difference between memory cells and plasma cells listed in our answer choices is that plasma cells are short-lived, whereas memory cells remain in the circulation for a longer time period. This tells us that the correct answer is option (A). Memory cells remain in the circulation for a longer time period.