Question

Draw graphs to compare the levels of RAG/VDJ and RAG/VJ complexes in double-negative, double-positive, and single positive T cells.

This is a question from my immunology class- I don't understand, please help!

Answer 1

ANSWER :-

1. There are certain point that I need to mention. First is that we have to classify which cells are found prominently and which are found in relatively less amounts. The T-cells namely the double positives (CD4+/CD8+) are the ones which are found abundantly followed by the single positives (CD4-/CD8+). The cells which are precursors to both are the double negative T-lymphocytes.
2. RAG also called as the Recombination Activating Genes play a vital role in creating double stranded breaks/nicks by means of cleaving a sequence that is associated with the binding of various factors that are associated with initiation of the recombination event responsible for creating the nicks and thereby cleavage of the various elements associated with the Variable (V), Diversity (D) and the Joining region (J) thereby leading to variations in binding specificity.
3. Taking into consideration that the VDJ recombination is seen in case of the heavy chain regions and the VJ recombination is associated with the light chain region of the peptide chain which are basically present in the B-cell which can be considered as the immunoglobulin cell. This is a major point in question how the event is linked to the thymocytes although it also indicates the presence in the T-cell receptor which in turn is associated with binding specificity for a particular T-lymphocyte which in turn is dependent upon the type of antigen binding to the receptor to mediate a response. But, it should be the double negative cells which should show maximum recombination frequency as these are the immature cells being formed prior to their maturation in the thymus into the fully matured single-positive T-lymphocyte. So, in short the frequency of recombination decreases as the cell matures and thus specificity increases.