What are lymphocytes ?
Lymphocyets are a another type of WBCs. Functionally there are 2 types- T and B lymphocytes. Also there is another type called natural killer cells which kill virally infected cells. T cells mature in thymus gland. B cells mature in bone marrow and final development continues in lymphoid tissue.
Phagocytic cells trap foreign antigens and present them to lymphocytes which involve in adaptive immunity.
T cells are involved with a and release substances which kill affected cells.
B cells are involved with humoral immunity and produce antibodies to attack antigens. 85% 0f circulating lymphocytes are T cells or Natural killer cells.
Normal range
 It is about 1 – 4.8 X109/ L of blood. As a percentage 26%-40% of total WBCs.
However, this may vary according to a person’s age, gender, lifestyle habits.
Morphology
They are the smallest type of WBC.
They have a small spherical nucleus which filled with dark stained chromatin. Size is similar to RBC size( it means 7 – 8μm)
But 10% of circulating lymphocytes are larger than that of small lymphocytes. The round nucleus is covered with thin rim of pale blue cytoplasm.
Why and When High Lymphocyte counts ?
When absolute count is over 4×109 /L it is called as Lymphocytosis.
Commonly seen in certain infections such as Viral infections, Infectious mononucleosis, brucellosis & tuberculosis. Also high lymphocyte counts can be seen in cronic lymphocytic leukemia & Non hodgekin’s lymphoma.
Why and When Low Lymphocyte counts ?
This is called as lymphocytopenia and it could be due to either acquired or inherited diseases. Examples include inherited disease called ataxia-telangiectasia, multiple sclerosis, auto immune disorders, AIDS and other infections.
Tests available
Differential white blood cell count can be used to check the person’s absolute lymphocyte counts. And it is easy to identify lymphocytes in stained blood smear due to its size and shape.
Flowcytometric analysis can be used to identify the different type of lymphocytes based on their antigen expression patterns.
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