White Blood Cells and Their Functions

Normal White Blood Cell Count

  • Normal range for white blood cells is between 5,000 and 11,000 cells per microliter of blood (5-11).

  • A count below 4,800 indicates insufficient white blood cells to fight infections, increasing the patient's risk of infection.

  • In immunocompromised patients with low white blood cell counts, neutropenic precautions are necessary.

Neutropenic Precautions

  • When a patient is immunocompromised, certain precautions must be taken to protect them.

  • Hospital precautions vary based on the infection type:

    • Airborne precautions

    • Droplet precautions

  • For neutropenic patients, healthcare providers must protect the patient from potential infections they could bring into the room.

  • Before entering the patient's room, healthcare providers must gown up, mask up, and glove up.

White Blood Cell Count and Infection

  • High white blood cell counts can indicate infection, typically ranging from 18,000 to 20,000 white blood cells during an infection.

  • Monitoring the labs periodically is important to track the response to antibiotics:

    • Labs are generally taken early in the morning (around 07:00) and may be repeated throughout the day as ordered by doctors.

    • A successful treatment should show a decrease in white blood cell counts over time; if counts do not decrease, this signals a red flag to the healthcare provider.

White Blood Cells Function

  • White blood cells play a crucial role in defending the body against disease.

  • They circulate through the bloodstream but can migrate to tissues during an infection.

  • When an injury occurs (e.g., a bite), the immune system sends cells and chemicals to the infected site.

Diapedesis

  • Diapedesis is the process by which white blood cells leave the capillaries to reach the site of infection.

    • The term "diapedesis" comes from the Greek word "podes" (meaning "foot").

    • White blood cells crawl out of blood vessels via diapedesis through a mechanism that slows them down, allowing them to adhere to the walls of capillaries and squeeze through into surrounding tissues.

    • White blood cells move via a process called amoeboid movement, initially described in amoeba.

Chemotaxis

  • Chemotaxis is the method by which white blood cells are directed to the site of infection.

    • The cells follow chemical signals (like a breadcrumb trail) emitted by damaged tissues or pathogens.

    • Positive chemotaxis refers to the movement toward increasing concentrations of these chemicals.

    • This concept is also critical in fetal development, where cells use chemotaxis to reach their designated locations.

Leukocytosis

  • A white blood cell count exceeding 11,000 cells per microliter of blood is termed leukocytosis.

    • The suffix "osis" denotes an abnormal increase.

    • Leukocytosis represents a normal response to infection.

Types of White Blood Cells

  • White blood cells are categorized into two groups:

    • Granulocytes

    • Agranulocytes

  • Granulocytes contain granules and include:

    • Neutrophils

    • Eosinophils

    • Basophils

  • Agranulocytes lack granules and include:

    • Lymphocytes

    • Monocytes

Staining and Identification of White Blood Cells

  • White blood cells stain differently under microscopic examination, depending on their granule composition:

    • Eosinophils stain red/orange with acidic dye eosin.

    • Basophils stain dark purple with basic dyes.

    • Neutrophils stain neutral due to a mix of granule contents.

Granulocytes

  • Neutrophils:

    • Account for 50-70% of total white blood cells.

    • About twice the size of red blood cells.

    • Have multi-lobed nuclei and polymorphonuclear structure, hence the abbreviation PMNs or polys.

    • Main function: phagocytosis of bacteria via a mechanism called respiratory burst, producing substances like bleach and hydrogen peroxide to kill microbes.

    • Defensins from granules fuse with phagosomes to kill engulfed pathogens.

  • Eosinophils:

    • Comprise 1-4% of white blood cells and possess a bi-lobed nucleus and reddish/orange granules.

    • Function: combat parasites and are reactive during allergic reactions.

    • Increase in eosinophils can indicate infections caused by parasites, allergies, or asthma.

  • Basophils:

    • The rarest white blood cells, making up less than 1%.

    • Possess dark purple granules that can obscure the nucleus, which contains histamine, a chemical mediator in allergic responses and inflammation.

Agranulocytes

  • Lymphocytes:

    • Large dark nuclei take up most of the cell; cytoplasm is thin and light blue.

    • Divided into T-cells (involved in anti-viral and anti-tumor responses) and B-cells (produce antibodies after activation).

    • T-Helper cells are significantly impacted by HIV, leading to severe consequences for immune function.

  • Monocytes:

    • The largest white blood cells, featuring a U-shaped or kidney-shaped nucleus.

    • Differentiate into macrophages in tissues, where they play roles in chronic infections and cleaning up debris.

Complete Blood Count (CBC)

  • A CBC provides an overview of blood cell levels, including white blood cells, red blood cells, and platelets.

  • A CBC with differential (CBC with diff) assesses the specific types and percentages of various white blood cells.

  • A Complete Metabolic Panel (CMP) or Basic Metabolic Panel (BMP) may be ordered for further insight into electrolyte levels and other bodily functions.

Historical Context of HIV/AIDS

  • The awareness of HIV/AIDS emerged prominently in the late 1970s and early 1980s, initially clouded by misunderstanding about its transmission methods.

  • Effective prevention strategies and treatments for HIV have significantly evolved since then, allowing for maintaining undetectable viral loads in patients.