MLAB 1415: Hematology Keri Brophy-Martinez Leukocytes- The Lymphocytes Part Three Differentiation & Maturation Develop from HSC (hematopoietic stem cell) Common lymphoid progenitor cell (CLP) gives rise to the committed precursor cells: o T lymphocytes (60-80% of lymph population) o B lymphocytes (10-20%) o Thymus Bone marrow Natural killer cells (NK) (~ 2 %) • Bone marrow or thymus Lymphopoiesis Primary lymphoid tissue Bone marrow, thymus, fetal liver Secondary lymphoid tissue ◦ Lymph node, spleen, Peyer’s patches in intestine and mucosal tissues such as tonsils ◦ Active immune response occurs in above tissues where lymphs communicate and interact with antigen-presenting cells, phagocytes and macrophages Lymphocyte Population Reference range= 1.0- 4.8 x 109/L Lymphocytosis ◦ Increase in lymphocytes ◦ Absolute number exceeds 4.8 x 109/L Lymphocytopenia ◦ Decrease in lymphocytes ◦ Absolute number of lymphocytes is <1.0 x 109/L Lymphocytes: T cells ◦ Function Cellular immune response (they do not produce antibodies) Three subsets Helper T cells Instrumental in aiding B cells in antibody production Turn on immune reponse Effected by Human Immunodeficiency Virus (HIV) Suppressor T cells Act as a “thermostat” to shut off the system or keep it under control Cytotoxic T cells Destroy by lysis of target cells (such as tumor cells) Play a role in inflammatory response Host defense when stimulated by interferon against certain viruses (cytomegalovirus - CM, and hepatitis) by killing the virally infected target cell before the virus replicates Responsible for chronic organ graft rejection. (T cells have many unique antigens on their cell surfaces, some of which are the HLA - human lymphocyte antigen - markers. HLA markers are instrumental in chronic graft rejection and that is why tissue typing is done to establish a good donor match.) Lymphocytes: B cells Function Humoral immune response by transforming into antibody-producing plasma cells Defense against encapsulated bacteria such as Streptococci Mediate hyperacute organ rejection Lymphocytes: Natural Killer (NK) cells Function ◦ Recognize and kill tumor cells ◦ Recognize and kill cells infected with a virus Maturation sequence of lymphocytes Lymphoblast ◦ Cell size: 10-18µm ◦ Cytoplasm Blue/scanty No granules, Auer rods are never present ◦ Nucleus Purple, smooth chromatin Smudged Round, central or eccentric 1-2 nucleoli ◦ N:C ratio = 4:1 Maturation sequence of lymphocytes Prolymphocyte ◦ Size: 9-18µm ◦ Cytoplasm Blue, scanty Usually granules are absent, but a few azurophilic granules may be present ◦ Nucleus Purple, condensed chromatin Round or indented, eccentric 0-1 nucleoli ◦ N:C ratio = 3:1 Maturation sequence of lymphocytes Mature lymphocyte ◦ Normal adult value: 25-35% Cell size: 7-10µm (a typical normal lymph has a nucleus that is the size of a normal RBC) ◦ Cytoplasm Light blue, scanty to moderate Few azurophilic granules may be present ◦ Nucleus Purple, dense, clumped chromatin Round or indented, eccentric No nucleoli Lymphocyte Maturation sequence Large lymphocytes versus monocytes Size ◦ Large lymph: 12-15µm ◦ Mono: 15-18µm Nucleus ◦ Large lymph: clumped, condensed ◦ Mono: lacy, brainlike folds Granules ◦ Large lymph: large azurophilic, easy to count ◦ Mono: red, fine Cytoplasm ◦ Large lymph: clear to light blue color, may be indented by red cells ◦ Mono: “ground glass” appearance, projection of blunt pseudopod blebs Large granular lymphocyte Monocyte Comparison of LGL and Monocyte Lymphocytic Variants Varied appearance Depends on degree of activation Many names ◦ Reactive ◦ Transformed ◦ Variant ◦ Atypical ◦ Downey cell Nomenclature varies depending on individual facilities Lymphocytic Variants Cause ◦ Caused by antigenic stimulants such as viruses, posttransfusion reactions and organ transplants General characteristics ◦ Increased size due to DNA activity in the nucleus and RNA activity in the cytoplasm ◦ Enlarged and/or monocytoid nucleus ◦ Variation in nuclear chromatin pattern ◦ Nucleus may contain 1-3 nucleoli ◦ Abundant, sometimes foamy or vacuolated cytoplasm ◦ Variation in cytoplasmic color - gray-blue to intense blue ◦ Absence of granules in cytoplasm Reactive lymphocytes Plasma cells • Function is the synthesis and excretion of antibodies (immunoglobulins) • Normally not present in the peripheral blood; comprise 2% of bone marrow cells. o EXCEPT in the disease called multiple myeloma, a disease of uncontrolled production of immunoglobulins. • End stage of the B lymphocyte • Appearance o Size: 10-18µm o Cytoplasm is dark blue with perinuclear halo and may contain vacuoles indicating antibody synthesis o Nucleus is round, eccentric, dark purple with dense clumped chromatin • Variant plasma cells o Grape or Mott cell - cytoplasm completely filled with red, pink or colorless globules called Russell bodies o Flame cell - cytoplasm stains bright red-staining proteinaceous material Plasma cells References Carr, J. H., & Rodak, B. (2009). Clinical Hematology Atlas. St. Louis: Saunders. Harmening, D. M. (2009). Clinical Hematology and Fundamentals of Hemostasis. Philadelphia: F.A Davis. McKenzie, S. B., & Williams, J. L. (2010). Clinical Laboratory Hematology . Upper Saddle River: Pearson Education, Inc.