Figure 3.

The balance of reactivity to self or antigen pMHCII complexes. The TCR of a given T cell may have high (red) or low (blue) affinity for self pMHCII (left side of the cell) or a particular antigenic pMHCII complex (right side of the cell). High affinity to either of these contributes positively to clonal expansion. (A) When all four possible (simplified) combinations are present, the clonotype that combines high affinity for self and for antigenic pMHCII will prevail. Selection of such clonotypes from large enough repertoires may create the impression that high affinity to self and antigen are positively correlated. (B) Between two clonotypes with equal affinity to self, the one with higher affinity to antigen will prevail. (C) Between two clonotypes with equal affinity to antigen, the one with higher affinity to self will prevail. (D) The outcome of competition between clonotypes one of which is high affinity for self and the other for antigen is currently difficult to predict.