Question

B cell activation requires (select ALL that apply): O T cytotoxic cells O Tcell receptor (TCR) binding to antigen displayed in MHC-|| O antigen binding to antibody on B cell surface T cell receptor (TCR) binding to antigen displayed in MHC-I Question 3 1 pts Which statement(s) about C proteins in the complement system is true (select ALL that apply): Cproteins are always active as they circulate through the body All of the C proteins are equally important for all aspects of complement activity C3 is a key protein for all aspects of complement activity They are normally in an inactive state There are nine C proteins (C1-C9)

Answer 1

For the first question:

B cell activation requires-

1. T cell receptor binding to antigen displayed in MHC-II

This is because B cells are activated with the help of T helper cells(TH) which are in turn associated with MHC-II .

For the second question:

Statements true for C proteins-

1. C3 is the key protein for all aspects of complement activity
2. They are normally in inactive state

There are more than 30 C proteins present in the complement system including C1-C9 and also letter symbols like Factor D or HRF. So we cannot say that there are only 9 C proteins present. Also the C proteins gets activated once they come in contact with the microbial cell surface or foreign antigens but not otherwise. The different C proteins are helpful in different aspects of complement system and not all are necessary for every pathway.