Basophils and Eosinophils

Summary

This video tutorial dives into the characteristics and functions of basophils and eosinophils, two important immune cells. Basophils, similar to mast cells, play a crucial role in allergic reactions and immune responses by releasing mediators like histamine and cytokines. Eosinophils, with their unique granules, are involved in extracellular killing, phagocytosis, and contribute to conditions like asthma, allergies, and parasitic infections. The tutorial highlights their involvement in both immediate and late-phase hypersensitivity reactions, as well as their role in diseases like rheumatoid arthritis and cancer.

Takeaways

• 😀 Basophils are small granulocytes with a segmented nucleus and large granules. They are key players in allergic reactions and immune responses.
• 😀 Basophils are activated via IgE interaction with FcεRI receptors, leading to degranulation and the release of histamine and other mediators like leukotrienes.
• 😀 Unlike mast cells, basophils have limited proliferative capacity but are critical for immediate hypersensitivity reactions like anaphylaxis.
• 😀 Basophils play a central role in both early and late-phase allergic reactions, influencing conditions like asthma, allergic rhinitis, and autoimmune diseases.
• 😀 IL-4 and IL-13 produced by activated basophils are crucial for Th2 cell differentiation, promoting allergic inflammation.
• 😀 Eosinophils contain granules filled with cationic proteins, including major basic protein (MBP), eosinophil peroxidase (EPO), and eosinophil cationic protein (ECP), which aid in pathogen destruction.
• 😀 Eosinophils play a major role in asthma and other allergic conditions by releasing cytotoxic proteins and inflammatory mediators.
• 😀 Eosinophils express a variety of receptors that regulate their activation, including those for cytokines like IL-3, IL-5, and GM-CSF, as well as complement and immunoglobulin receptors.
• 😀 Eosinophilia, or elevated eosinophil counts, can occur in response to allergies, infections (especially parasitic), autoimmune diseases, and certain cancers.
• 😀 Eosinophils are involved in both intracellular killing of pathogens and extracellular mechanisms such as degranulation and DNA trap formation.
• 😀 Both basophils and eosinophils are implicated in chronic diseases and hypersensitivity reactions, contributing to conditions like rheumatoid arthritis and eosinophilic disorders.

Q & A

What is the size of basophils, and how are they identified?

Basophils are 5–8 micrometers in diameter and can be identified using basic stains such as toluidine blue or Alcian blue.

How do the granules in basophils differ from those in mast cells?

Basophils have fewer, but larger granules compared to mast cells (MCs).

What receptors do basophils express, and what are their roles?

Basophils express various receptors, including cytokine receptors (IL-3R, IL-5R, GM-CSFR), chemokine receptors (CCR2, CCR3), and immunoglobulin receptors (FcεRI, FcγRIIb), among others. These receptors play a role in basophil activation, recruitment, and cytokine production.

How are basophils activated, and what role do IgE and complement proteins play?

Basophils are activated by IgE binding to FcεRI receptors, similar to mast cells. Complement proteins C3a and C5a also activate basophils through their respective receptors.

What are the key mediators released by activated basophils?

Activated basophils release histamine, cysteinyl leukotrienes (LTC4, LTD4, LTE4), and cytokines such as IL-4, IL-13, and GM-CSF.

What role do basophils play in hypersensitivity reactions?

Basophils are involved in immediate hypersensitivity reactions (e.g., anaphylaxis) by degranulating in response to allergens. They also participate in late-phase hypersensitivity reactions, such as allergic rhinitis and severe asthma.

How do basophils contribute to delayed hypersensitivity reactions?

In delayed hypersensitivity reactions, basophils are the predominant granulocytes, with the peak reaction occurring 2–3 days after allergen exposure. They promote a Th2-polarizing microenvironment through IL-4 and IL-13 production.

What diseases are basophils implicated in beyond hypersensitivity reactions?

Basophils are implicated in diseases such as rheumatoid arthritis, helminth infections, and certain cancers like chronic myeloid leukemia.

What are the main characteristics of eosinophils?

Eosinophils have a bi-lobed nucleus with condensed chromatin. They contain specific and primary granules, and lipid bodies form rapidly after eosinophil activation.

What are the major proteins found in eosinophil granules, and what do they do?

The major proteins in eosinophil granules are major basic protein (MBP), eosinophil peroxidase (EPO), eosinophil cationic protein (ECP), and eosinophil-derived neurotoxin (EDN). These proteins help with cytotoxicity and defense against pathogens.

What role do eosinophils play in allergic diseases like asthma?

Eosinophils are key players in asthma, often contributing to airway inflammation and eosinophilia, which can exacerbate the condition. They release inflammatory mediators such as leukotrienes and cytokines.

What are some of the causes of eosinophilia, and how can it manifest in different diseases?

Eosinophilia can be caused by infections (e.g., parasitic), allergies, autoimmune disorders, and neoplastic conditions. It can lead to organ dysfunction and manifest in diseases such as asthma or eosinophilic disorders.

How do eosinophils contribute to both innate and adaptive immune responses?

Eosinophils participate in innate immunity by phagocytosing pathogens and releasing cytotoxic granules. They also play a role in adaptive immunity by presenting antigens and modulating T-cell responses, especially in allergic reactions.