Lymph nodes contain specialized compartments where immune cells congregate, and where they can encounter antigens. Cells of the Immune System Cells destined to become immune cells, like all blood cells, arise in the bone marrow from so-called stem cells. Other myeloid descendants become granule-containing inflammatory cells such as eosinophils and basophils. Lymphoid precursors develop into the small white blood cells called lymphocytes. The two major classes of lymphocytes are B cells and T cells.
B cells work chiefly by secreting soluble substances known as antibodies.
Each B cell is programmed to make one specific antibody. Each plasma cell is essentially a factory for producing that one specific antibody. It is these unique contours in the antigen-binding site that allow the antibody to recognize a matching antigen, much as a lock matches a key. The stem of the Y links the antibody to other participants in the immune defenses. IgG, IgD, and IgE Antibodies belong to a family of large protein molecules known as immunoglobulins.