Final answer:
Pattern Recognition Receptors (PRRs) are germ line-encoded receptors that recognize common pathogen structures, as opposed to T-cell receptors (TCRs) and B-cell receptors (BCRs), which undergo genetic rearrangements for antigen receptor diversity.
Step-by-step explanation:
The question is asking about which class of cell surface receptors are encoded directly in the germ line without the need for genetic rearrangement. The correct answer is Pattern Recognition Receptors (PRRs). PRRs are germ line-encoded receptors that recognize pathogens by identifying pathogen-associated molecular patterns (PAMPs) common to a group of viruses, bacteria, parasites, or fungi. Unlike PRRs, T-cell receptors (TCRs) and B-cell receptors (BCRs) undergo a genetic rearrangement process to create diversity in antigen recognition. TCR diversity is created through the rearrangement of Variable (V), Diversity (D), and Joining (J) gene segments, whilst BCRs (which also function as membrane-bound antibodies such as IgD and IgM) also rearrange these segments to provide millions of unique antigen-binding sites. Thus, the receptors themselves are not directly germ line-encoded but rather result from this highly variable process.