Final answer:
Lymphocytes, specifically B cells and T cells, are the primary cells of adaptive immunity, involved in antibody production and direct cell attack, respectively.
Step-by-step explanation:
The primary cells of adaptive (specific) immunity are lymphocytes, which include B cells and T cells. B cells are responsible for producing antibodies, a process known as humoral immunity, while T cells attack infected cells directly, which is referred to as cellular immunity. Natural killer (NK) cells, although a type of lymphocyte, provide generalized, nonspecific immunity and are not the primary cells of adaptive immunity. Instead, NK cells are considered a part of the innate immune system. The two basic types of lymphocytes responsible for adaptive immunity are distinguished by their surface protein markers and the molecules they secrete, with B cells maturing in the red bone marrow and T cells maturing in the thymus.