WBC Basics

Now that we’ve gone over the basics of where cells come from let’s dive into normal lab values for some of these cell types.

Normal ranges for WBCs as a percentage of the total WBC count:
Neutrophils: 50-70%
Bands: 2-6%
Monocytes: 2-9%
Eosinophils: 0-4%
Basophils: 0-2%
Lymphocytes: 20-44%
Lymphocytes (babies): 50-70%
Blasts: 0%

We already know the main function of RBCs is to transport O₂ to tissues and facilitate CO₂ excretion. What is the main function of these other cells?

Neutrophils:
Neutrophils are first responders of the blood stream and of the innate immune system. They will quickly mobilize to a site of injury and one of their main functions is to destroy invading bacteria or fungus by phagocytosis. They are the most common WBC at 50-70%.

Nerdy Note
Other than phagocytosis, neutrophils have an alternate way of killing bacteria, neutrophilic extracellular traps (NETs). Neutrophils will shoot out a net-like structure of DNA and granule proteins which will trap the microbe. It is thought it may be used as a last resort attempt at controlling a potential pathogen. Talk about taking one for the team!

Perspective Note
Neutrophils have a short lifespan, some estimate it to be less than a day while others have it at about 5 days. Due to the quick turnover rate, the average person will make around 500 billion neutrophils a day! Even on Sunday!

Bands:
Bands usually refers to the amount of band neutrophils in the peripheral blood. It can also refer to basophils or eosinophils but this is less common. The band neutrophil is a slightly immature neutrophil and it’s normal to have 2-6% of your WBCs as this cell type.

Basophils:
Basophils are involved in the inflammation process, and are most commonly known to contribute to acute and delayed allergic reactions. They are known to contain antihistamine and heparin. They are far fewer in number than neutrophils.

Eosinophils:
Eosinophils are most commonly known for their ability to fight parasitic infections. They are slower travelers, taking days in some cases to reach the affected tissue. They contain large granules and are known for their orange color on a Wright stain peripheral smear.

Monocytes:
When monocytes leave the bloodstream they grow into macrophages. Macrophages have many functions and one of the main ones is debris cleanup. Macrophages phagocytose cellular debris, dead cells, bacteria, and even things like dead neutrophils. They’re like a security guard – trash collector hybrid. As you may recall from the coagulation section, macrophages will remove broken down fragments of a fibrin clot. Everything is connecting together! The Infinity Gauntlet of understanding is within reach! Macrophages can also be involved in antigen presentation (more on this later).

Lymphocytes:
Behind neutrophils, lymphocytes are the second most abundant WBC. Characteristically, they can vary in size, have a high N:C ratio (nuclear to cytoplasm ratio) meaning it’s mostly nuclear, and have clumped chromatin. It is important to understand the basic differences between the types of lymphocytes mainly the T-cells and B-cells.

T-cells:
T-cells mature in the thymus and are a major player of the adaptive immune system. T-cells can be divided up into “helper” T-cells (CD4+) and “cytotoxic” T-cells (CD8+). Helper T-cells help activate the immune system when an antigen presenting cell (APC) such as a macrophage or dendritic cell presents the T-cell with a peptide antigen and an MHC class II molecule. Through cytokine release and other complex biochemical processes, CD4+ T-cells can help orchestrate attacks on pathogens.

There are many subtypes of CD4+ T-cells such as Th1, Th2, Th17, and Treg, all which have enormous complexity. CD4+ T-cell subtype differentiation is determined in large part by the antigen presented to the T-cell. The T-cell is like a football coach who when presented with certain information about the opposition will deploy different strategies and combinations of players to fight the opponent.

Nerdy Note:
The importance of CD4+ T-cells can’t be understated and this becomes extremely apparent in the disease HIV/AIDS. The virus in this condition attacks CD4+ T-cells, and when the count is less than 200/uL (normal is 500-1500/uL), the patient is diagnosed with AIDS. CD4+ T-cells are vital for life.

Cytotoxic T-cells (CD8+) destroy cancerous and other infected or malfunctioning cells. Cytotoxic T-cells bind an antigen and an MHC class I molecule. MHC class I molecules are present on all nucleated cells.

B-cells:
B-cells mature in the bone marrow and are also a major player of the adaptive immune system. B-cells can become plasma cells which are antibody producing cells. Basically, each B-cell has a unique receptor and when that receptor comes in contact with its matching pathogen it will create an antibody response. B-cells are the precise specialists of the immune system.

Natural Killer (NK) cells:
NK cells play an important role in the innate immune system. Much like cytotoxic T-cells, they are able to destroy cancerous and other malfunctioning cells as well as invading pathogens. NK cells are also able to destroy these pathogens without a specific receptor and they are able to act quickly.