Which lymphocyte type is involved in carrying antibodies or receptors specific to antigens?

Memory cells are a type of lymphocyte that play a crucial role in the adaptive immune response by carrying antibodies or receptors specific to previously encountered antigens. When the immune system is exposed to a pathogen for the first time, it generates specific antibodies against that pathogen. Once the pathogen is cleared, a subset of those activated B cells becomes memory cells. These memory cells persist in the body and are able to quickly recognize and respond to the same antigen if encountered again in the future, which provides long-lasting immunity.

In contrast, macrophages are a type of immune cell that engulf and digest pathogens but are not specific in their response to antigens, nor do they carry antibodies. T lymphocytes primarily have roles in killing infected host cells and modulating the immune response, but they do not primarily carry antibodies like B cells and memory cells. Pathogens are the harmful agents targeted by the immune response, but they do not have the capability to carry antibodies or receptors. Thus, memory cells standing out as the correct answer emphasizes their specific function in retaining information about past infections and generating a robust response upon re-exposure to a familiar antigen.