Question

Like T cells, B cells require multiple signals for activation. Antigen binding to the B cell antigen __________provides one signal, while antigen-specific effector ________ provide the other signals. The requirement for multiple signals to activate either a T cell or a B cell helps to prevent _______ and dangerous activation of _________ , including  __________ _________. Most of the proteins involved in cell–cell recognition and antigen recognition in the immune system, including  _________ , TCRs, and  _______ proteins, as well as various co-receptors, belong to the ancient Ig superfamily. This superfamily is thought to have evolved from a primordial gene encoding a single Ig- like  _______ . The mechanisms for diversifying antibodies and T cell receptors by recombining gene segments may have arisen when a  _________ inserted into an exon of a gene encoding an Ig family member.

receptors (BCRs)    helper T cells                        killer T cells
inappropriate                          appropriate                           monocytes
lymphocytes                          self-reactive                           non-self-reactive
antibodies                              IPR                                        MHC
domain                                  transposon                            retrovirus

Answer 1

Antigen binding to the B cell antigen receptors (BCRs) provides one signal, while antigen-specific effector helper T cell provides the other signals. The requirement for multiple signals to activate either a T cell or a B cell helps to prevent inappropriate and dangerous activation of lymphocytes including killer T cells. Most of the proteins involved in cell–cell recognition and antigen recognition in the immune system, including antibodies, TCRs, and MHC proteins, as well as various co-receptors, belong to the ancient Ig superfamily. This superfamily is thought to have evolved from a primordial gene encoding a single Ig- like domain. The mechanisms for diversifying antibodies and T cell receptors by recombining gene segments may have arisen when a transposon inserted into an exon of a gene encoding an Ig family member.