Lymphocytes are a type of white blood cell (leukocyte) that play a central role in the body’s immune system, particularly in defending against infections and foreign substances.
They are primarily found in the lymphatic system, which includes the lymph nodes, spleen, and thymus.
Origin and maturation: Formed in the bone marrow and mature there.
Function: Responsible for humoral (antibody-mediated) immunity.
Action:
When activated by an antigen, B cells differentiate into:
Plasma cells, which produce antibodies that bind to specific antigens (e.g., bacteria, viruses, toxins).
Memory B cells, which remain in the body to mount a faster, stronger response upon future exposure to the same antigen.
Origin and maturation: Formed in the bone marrow but mature in the thymus.
Function: Responsible for cell-mediated immunity — directly attacking infected or abnormal cells, and regulating immune responses.
Subtypes:
Helper T cells (CD4+):
Coordinate the immune response by secreting cytokines that activate other immune cells (B cells, cytotoxic T cells, and macrophages).
Cytotoxic T cells (CD8+):
Destroy virus-infected cells, tumor cells, and cells from transplanted tissues.
Regulatory (suppressor) T cells:
Help prevent autoimmune reactions by suppressing overactive immune responses.
Memory T cells:
Provide long-term immunity by responding rapidly to previously encountered antigens.
Function: Part of the innate immune system (non-specific defense).
Action:
Destroy virus-infected or cancerous cells without prior sensitization.
Recognize cells lacking normal “self” markers (such as MHC class I molecules).
| Type | Maturation Site | Main Function | Immune Type |
|---|---|---|---|
| B cell | Bone marrow | Produces antibodies; humoral immunity | Adaptive |
| Helper T cell | Thymus | Activates B and T cells; releases cytokines | Adaptive |
| Cytotoxic T cell | Thymus | Kills infected or abnormal cells | Adaptive |
| Regulatory T cell | Thymus | Suppresses immune overactivity | Adaptive |
| NK cell | Bone marrow | Kills virus-infected and tumor cells | Innate |
In short, lymphocytes are the body’s key defense cells, working together to recognize, attack, and remember harmful invaders—forming the basis of both innate and adaptive immunity.