Which one of the combinations of the following statements is true about antibody structure?<br>P. Limited proteolysis of rabbit IgG with the enzyme pepsin generates two antigen-binding regions (Fab) and an Fc fragment.<br>Q. Limited proteolysis of rabbit IgG with the enzyme papain generates a single bivalent antigen-binding region F(ab')<sub>2</sub> and peptide fragments.<br>R. The Fc fragment of IgG can self-associate and crystallize into a lattice.<br>S. The F(ab')2 fragment of IgG is composed of both light and heavy chains.

Correct Answer: R and S only