Home / Life Science / Types of White Blood Cells (Leukocytes) With Their Structure and Functions

Types of White Blood Cells (Leukocytes) With Their Structure and Functions

White blood cells (WBCs), or leukocytes, are a heterogeneous group of immune cells that helps our body to fight against infections. They are found throughout the body, i.e., connective tissue, bloodstream, and lymphatic system. WBCs are produced from specialized multipotent stem cells present in the bone marrow, commonly known as hematopoietic stem cells.

All WBCs are nucleated cells that distinguish them from non-nucleated blood cells, i.e., Red blood cells (RBCs) and platelets. Normal WBC count is usually between 4 × 109/L and 1.1 × 1010/L, which constitute approximately 1% of the total blood volume, thus about 45% less numerous compared to RBCs.

What are the different types of white blood cells in the human body?

Based on structure, white blood cells are classified into two types:

  • Granulocytes – WBCs, having granules in the cytoplasm.
  • Agranulocytes WBCs, having no distinct granules in the cytoplasm.

Broadly white blood cells can be divided into the five following types:

1. Neutrophils or Polymorphonuclear (PMN) leukocytes (Granulocytes)

— Structure

Has a multi-lobed nucleus (generally consisting of three to five lobes) with each lobe being connected by thin strands, making it look multinucleated. Inactivated neutrophils are spherical, but once activated, they take on an amoeba-like appearance. These granulocytes have an average diameter of 12-15 µm in the peripheral blood, while in suspension, they have a diameter of 8.85 µm.

— Abundance

Constitutes 62% of the total leukocyte count

— Composition

The cytoplasm of a neutrophil looks transparent because of the presence of fine granules. Other organelles like the Golgi apparatus, mitochondria, and ribosomes are also present.

— Lifespan

Can vary vastly between 5 to 135 hours

— Functions

  • Consuming and digesting pathogens like bacteria in a process to kill and present them in the form of pus (Performingphagocytosis). They produce superoxide radicals that help in the digestion of microbes.

2. Eosinophils (Granulocytes)

— Structure

The nucleus is bi-lobed, with the two lobes being connected by a thin-strand.  They are about 12-17µm in size. The cytoplasm of eosinophil is full of granules (almost 200).

— Abundance

Comprises about 2-4% of the total WBCs; their number is found to increase in response to any infections, especially parasitic infections.

— Composition

Acidic granules in the cytoplasm, which contains enzymes and proteins that take up pink-orange color when stained with eosin.

— Lifespan

Circulating half lifespan of approximately 18 hours; tissue life of 2 to 6 days

— Functions

  • Destroying large parasites such as hookworms and tapeworms, by secreting specific chemicals.
  • Having roles in case of allergic reactions such as asthma, hay fever, and infections of hives.

3. Basophils (Granulocytes)

— Structure

Having a bi- or tri-lobed nucleus, with the presence of large cytoplasmic granules. They are generally round but can change shapes as they migrate.

— Abundance

Accounts for only 0.5% of the total leukocyte count

— Composition

Sharing similar physicochemical properties with other white blood cells.

— Lifespan

About 60–70 hours

— Functions

  • Taking care of inflammatory reactions during an immune response. Inflammatory reactions by basophil are due to the release of immune-complexes like histamine, serotonin, and heparin (an anticoagulant that prevents blood clotting).
  • Producing the body’s response to specific allergic reactions, such as anaphylaxis, asthma, and hay fever.

4. Lymphocytes (Non-granulocytes)

— Types

Lymphocytes, with a diameter of 12-15 μm, are broadly classified into three types-

  • B cells or B Lymphocytes – identified by the presence of B cell receptor or BCR and belonging to small lymphocyte subtype.
  • T cells or T Lymphocytes – identified by the presence of T cell receptor or TCR (classified into CD4+ helper, CD8+ cytotoxic, and Regulatory T cells)
  • Natural killer cells (NK cells) – identified by the presence of CD3 receptor.

— Abundance

Comprising 30% of the total white blood cells; lymphocytes are much more abundant in the lymph nodes of the lymphatic system compared to blood

— Lifespan

Mostly have a short life span ranging from a week to a few months, but a few even live for years, thus providing immunological memory to certain infections.

— Functions

  • Providing body defense against infections through i) recognizing antigens, ii) producing antibodies and, iii) killing infected cells.
  • B cells produce antibodies which bind and attack pathogens and helps in its destruction.
  • T cells provide immunity from foreign pathogens through antibody-mediated response (adaptive immunity)
  • NK cells provide the first line of defense in our body (innate immunity) by destroying viral-infected cells and other harmful organisms. They also play a role in destroying cancer cells.

5. Monocytes (Non-granulocytes)

— Structure

Largest of all WBCs, resembling amoeba in appearance with unilobar nuclei and non-granulated cytoplasm. The nucleus of monocyte is typically bean- or kidney-shaped.

— Abundance

Consists of about 2 to 10% of the circulating white blood cells; this may increase in case of infections.

— Composition

Contains numerous fine granules that are most abundant near the cell membrane.

— Lifespan

About 24 hours

Functions

  • Having a similar role to neutrophils that work by phagocytosis.
  • Helping in the production of antibodies
  • Producing specific chemicals known as a cytokine to kill pathogens.
  • Antigen presentation with the help of specific receptors.

FAQs

Q.1. Which white blood cell is most abundant?

Neutrophil is the most abundant of all white blood cells, constituting 62% of the total leukocyte count.

Q.2. Which white blood cell is the least abundant?

Basophil is the least abundant of all white blood cells, accounting for only 0.5% of the total leukocyte count.

Q.3. Which is the largest white blood cell?

Monocytes are the largest of all white blood cells.

Q.4. Which is the smallest white blood cell?

Lymphocytes are the smallest of all white blood cells.

Article was last reviewed on Friday, December 6, 2019

Leave a Reply

Your email address will not be published. Required fields are marked *