T-cells are responsible for cell mediated immunity whereas B-cells are responsible for Humoral immunity (relating to antibodies). T-cells are named such because these lymphocytes mature in the Thymus and B-cells mature in bone marrow.
In the presence of an Antigen, B-cells become much more metabolically active and transform into Plasma cells. Plasma cells are large lymphocytes with a large nuclear to cytoplasmic ratio and are the form of B-cell lymphocytes that produce antibodies. Azurophilic granules are often present with an increase in cytoplasm.
Microscopically, in a Wright's stained peripheral blood smear, a normal lymphocyte has a large, dark-staining nucleus with little to no Basophilic cytoplasm. In normal situations, the coarse, dense nucleus of a lymphocyte is approximately the same size as a red blood cell (about 7 micrometres in diameter). Some lymphocytes show a clear perinuclear zone (or halo) around the nucleus or could exhibit a small clear zone to one side of the nucleus.
It is impossible to distinguish between T-cells and B-cells in a peripheral blood smear. Normally, Flow cytometry testing is used for specific lymphocyte population counts. When one must specifically determine the percentage of lymphocytes that produce a particular secretion (say, a specific antibody or cytokine), the ELISPOT technique can be used instead.
The Human Immunodeficiency Virus hijacks and destroys T-cell lymphocytes (specifically, CD4 lymphocytes). Without this key defense, the body is susceptible to opportunistic diseases that otherwise would not kill healthy people.
A lymphocyte count is part of a peripheral complete blood cell count and is expressed as percentage of lymphocytes to total white blood cells counted. An increase in lymphocytes is usually a sign of a viral infection (in some rare cases, leukemias are found through an abnormally raised lymphocyte count in an otherwise normal person). A general increase in the number of lymphocytes is known as Lymphocytosis whereas a decrease is lymphocytopenia.
| Immune system - Lymphatic system |
|---|
| Lymph nodes - Lymph - Lymphocytes - Lymph vessels - Thoracic duct |
| Bone marrow - Spleen - Thymus - Tonsils |
| Cardiovascular system - Blood |
| Red blood cells - White blood cells - Platelets - Blood plasma - Pluripotential hemopoietic stem cell |
| White blood cells |
| Granulocytes (Neutrophil granulocytes, Eosinophil granulocytes, Basophil granulocytes) - Lymphocytes - Monocytes |
| Coagulation |
| Coagulation factors: - Fibrin (I) - (Pro)thrombin (II) - FV - FVII - FVIII - FIX - FX - FXI - FXII - FXIII - HMWK - vWF - Tissue factor |
| Inhibitors: Antithrombin - Protein C - Protein S - Protein Z - ZPI - TFPI |
| Fibrinolysis: Plasmin - tPA/Urokinase - PAI-1/2 - α2-AP - TAFI |