How do white blood cells work to protect us?
White blood cells (leukocytes) protect the body against both infectious disease and foreign invaders.
Broadly, WBCS are categorized by structure (granulocytes or agranulocytes) or by cell lineage (myeloid cells or lymphoid cells). These broadest categories can be further divided into the five main types: neutrophils, eosinophils (acidophiles), basophils, monocytes, and lymphocytes. Bands are immature neutrophils.
These types are distinguished by their physical and functional characteristics. Monocytes and neutrophils are phagocytic. Further subtypes can be classified; e.g. among lymphocytes, there are B cells, T cells, and NK cells.
How do neutrophils kill microbes?
“Neutrophils provide the first line of defense of the innate immune system by phagocytosing, killing, and digesting bacteria and fungi”. Annual review of immunology.
e.g. Neutrophils kill bacteria by ingesting them. Neutrophils can ingest five to 20 bacteria in their lifetime.
How do monocytes-macrophages kill microbes?
Monocytes and neutrophils are phagocytic. Click here.
How do eosinophils work?
“Eosinophils are innate immune leukocytes found in relatively low numbers within the blood. Terminal effector functions of eosinophils, deriving from their capacity to release their content of tissue-destructive cationic proteins, have historically been considered primary effector mechanisms against specific parasites, and are likewise implicated in tissue damage accompanying allergic responses such as asthma. However, the past decade has seen dramatic advancements in the field of eosinophil immunobiology, revealing eosinophils to also be key participants in many other facets of innate immunity, from bridging innate and adaptive immune responses to orchestrating tissue remodeling events…
Eosinophils are innate immune granulocytes best recognized for their cytotoxic effector functions, causing damage to parasitic pathogens in helminth infections, and to host tissues in allergic diseases. However, more recent data have uncovered a much more complex picture, revealing additional roles for eosinophils in regulating inflammation, maintaining epithelial barrier function, affecting tissue remodeling, and bridging innate and adaptive immunity. Many of these functions arise from the capacity of eosinophils to store a preformed armamentarium of cytokines, chemokines and growth factors, available for immediate release.
Eosinophils are generally found in low numbers within circulation (1–4% of total peripheral blood leukocytes), while the majority of eosinophils at baseline reside within mucosal tissues interfacing with the environment and within primary and secondary lymphoid tissues. Localization to mucosal surfaces places eosinophils within ideal sites to identify and respond rapidly to pathogens, and within secondary lymphoid tissues, eosinophils are well-poised for their functions in bridging innate and adaptive immunity. Moreover, in response to allergens or Th2-inducing helminth infections, eosinophils are rapidly recruited to tissue sites.” Cell and tissue research.
“Eosinophils are granulocytes derived from the same progenitor cells as monocytes-macrophages, neutrophils, and basophils. They are a component of the innate immune system. Eosinophils have a variety of functions, including
Defense against parasitic infections
Defense against intracellular bacteria
Modulation of immediate hypersensitivity reactions
Eosinophils are especially important in defense against parasitic infections. However, although eosinophilia commonly accompanies helminthic infections and eosinophils are toxic to helminths in vitro, there is no direct evidence that they kill parasites in vivo.
Eosinophils may modulate immediate hypersensitivity reactions by degrading or inactivating mediators released by mast cells, such as histamine, leukotrienes (which may cause vasoconstriction and bronchoconstriction), lysophospholipids, and heparin. Prolonged eosinophilia may result in tissue damage by mechanisms that are not fully understood” Merk Manuals.
How do basophils work?
Basophils are “a type of immune cell that has granules (small particles) with enzymes that are released during allergic reactions and asthma”.
Basophils, like eosinophils, also function in allergic reactions. Basophils release histamine (which makes blood vessels leak and attracts white blood cells) and heparin (which prevents clotting in an infected area so that the white blood cells can reach the bacteria).
**Basophils work similar to eosinophils.
References and Resources
Segal AW. How Neutrophils Kill Microbes. Annual review of immunology. 2005;23:197-223.
Shamri R, Xenakis JJ, Spencer LA. Eosinophils in innate immunity: an evolving story. Cell and tissue research. 2011;343(1):57-83.
merckmanuals.com/professional/hematology-and-oncology/eosinophilic-disorders/eosinophil-production-and-function. Last Accessed 9/18/2018