IMAT 2018 Q37 [B Lymphocytes]

B lymphocytes are involved in the human immune response to a bacterial infection.

Which of the following processes would TYPICALLY be carried out by these lymphocytes in response to the infection?

  1. cell division by mitosis
  2. transcription producing mRNA
  3. engulfing and digesting bacteria

A. 1 and 2 only
B. 3 only
C. 1 and 3 only
D. 1 only
E. 2 and 3 only

The answer to this question is choice A, only statements 1 and 2 are correct.

Let us analyze each of the statements to discern if they are correctly associated with B lymphocytes.

  1. “cell division by mitosis”: B lymphocytes as you know, are a significant part of the innate immune system in response to infection or foreign microbes. The main inducer of the innate immune system is the antigen, or the substance that the immune system uses to identify infections. This recognition of antigen involves a lot of steps, but for relevancy with this question, do recall that it will lead to the clonal expansion of activated B cells, in other words, activated B cells will undergo mitosis to increase the number of B lymphocytes. This increase in B lymphocytes allow some to differentiate to plasma cells (that produce antibodies), and some differentiate to memory B cells, which are integral cells in identifying further infections of the same pathogen. Thus, this statement is a correct association with B lymphocytes.

  2. “transcription producing mRNA”: As you already know with the process of transcription, along with the process of translation, the main product is protein. How is protein relevant with B lymphocytes? Refer to the explanation to statement #1, and observe the mention of plasma cells that produce antibodies! Remember, that antibodies are immunoglobulins that are made of protein, which further supports that the presence of transcription in B lymphocytes is important in its function of producing antibodies against the foreign antigen. This makes it a correct association with B lymphocytes.

  3. “engulfing and digesting bacteria”: This is an incorrect association with B lymphocytes. But you might be wondering, “B lymphocytes CAN phagocytose, why is this statement wrong?” Keep in mind, that the question mentioned “…TYPICALLY be carried out …”. Thus, you need to discern whether the statements are TYPICALLY performed by B lymphocytes. Statements 1 and 2 are typically done by B lymphocytes since these are integral parts of their function. However, in terms of engulfing and digesting bacteria, or phagocytosis, are usually done by cells such as macrophages, monocytes, dendritic cells, and neutrophils. Thus, even though B lymphocytes CAN phagocytose, it does not mean they TYPICALLY do so, making this an incorrect association with B lymphocytes.

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