Question XII Similarities between TCRs and immunoglobulins i

Question XII. Similarities between TCRs and immunoglobulins include [in this context, assess the following statements (52-60) as either factually correct (= “true”) or incorrect (= “false”)]: 124. Three CDRs of the Va TCR domain and 3 CDRs of the Vb TCR domain are analogous to the CDRs of the VH and VL domains.

125. The TCR resembles the membrane-bound Fab fragment of immunoglobulin: an antigen-binding site, two variable domains, two constant domains.

126. Both of them undergo somatic hypermutation.

127. Both of them are generated through somatic recombination of sets of gene segments.

128. The constant regions of both of them have similar functions.

129. Both the T-cell repertoire and the B-cell repertoire is generated by the same molecular mechanisms (combining different gene segments, junctional diversity, etc.).

130. Both of them have 2 antigen-binding sites.

131. Both of them naturally occur in membrane-bound and secreted forms.
132. Like the variable regions of the heavy chain of the B-cell Ig receptor, TCR variable genes are all encoded in three segments.

Solution

ans.

125. True TCR resembles the membrane bound Fab fragment or immunoglobulin

he Fab fragment of antibody molecules is a disulfide-linked heterodimer, each chain of which contains one immunoglobulin C domain and one V domain; the juxtaposition of the V domains forms the antigen-binding site . The T-cell receptor is also a disulfide-linked heterodimer, with each chain containing an immunoglobulin C-like domain and an immunoglobulin V-like domain. As in the Fab fragment, the juxtaposition of the V domains forms the site for antigen recognition.

126. False since only Bcell undergoes somatic mutation and but Tcell recertor does not undergoes somatic muation

130. False since Tcell receptor has only one antigen binding site and B cell has 2 antigen binding site

131. False since T cells are always membrane bound form and never in secreted form whereas the B cells present as secreted as well as membrane bound form