Apa from B cells, and T cells, there is a 3rd distinct type of lymphocyte. This is:

Ans. (b) NK cell Ref. Dr Arora 3/e, p 156, p 127; Harrison 17/e, p 2024, 18/e, p 2651 I I I I Bone marrow Thymus Null Plasmacytoid B cell T cells Cells dendritic cells I____________________________ 'I I CD4 T-cell K-cell NK cell LAK cells NK/T cells (NK cells which express CD-3) A small propoion (5%) of lymphocyte that lack phenotypic markers B or T lymphocytes. A sub-opulation of null cell which has surface receptor for Fc pa of IgG. They are responsible for ADCC (antibody dependent cell mediated cytotoxicity). cells: These are large lymphocytes containing azurophilic granules in the cytoplasm. They are therefore cells known as large granular lymphocytes (LgL). LAK (Lymphocyte activated killer) cells are NK lymphocytes that proliferate in response to high concentration of IL-2 and develop the ability to kills tumor cell more efficiently. These are CD3 + ye NK cells, that can recognize lipid molecules of intracellular bacteria when presented in the context of CD-1 molecules on antigen presenting cells. These cells form an impoant defense against intracellular organism like histeria, mycobacterium.