INFLAMMATION 8: CHRONIC INFLAMMATION- Causes, Morphology & Cells

Summary

This tutorial from Pathology Made Simple provides an in-depth look at chronic inflammation, building on concepts from previous lessons on acute inflammation. The video covers the definition, causes, and morphological features of chronic inflammation, including the role of lymphocytes, macrophages, and other immune cells. It highlights key mechanisms such as tissue injury, repair, and the formation of lymphoid follicles. Additionally, the video explores the involvement of various cells, including CD4+ T cells, B cells, eosinophils, and mast cells in chronic inflammatory responses. The tutorial offers insights into how chronic inflammation develops and its impact on tissue.

Takeaways

• 😀 Chronic inflammation is a prolonged response, lasting weeks to months, that involves inflammation, tissue injury, and attempts at repair.
• 😀 Chronic inflammation may or may not follow acute inflammation, and it is not synonymous with chronic infection.
• 😀 The main causes of chronic inflammation include persistent infections, hypersensitivity diseases, and prolonged exposure to toxic agents (e.g., silica, cholesterol).
• 😀 Chronic inflammation can lead to tissue damage and repair processes like fibrosis (scar tissue formation) and angiogenesis (new blood vessel growth).
• 😀 In chronic inflammation, the primary cells involved are mononuclear cells such as macrophages, lymphocytes (B and T cells), plasma cells, and occasionally eosinophils.
• 😀 Lymphocytes, especially CD4+ T-helper cells, play a crucial role in chronic inflammation by amplifying the immune response and promoting the persistence of inflammation.
• 😀 CD4+ T-helper cells have subtypes (Th1, Th2, Th17) that release different cytokines, influencing macrophage activation and the recruitment of other immune cells like neutrophils and eosinophils.
• 😀 B cells are activated in chronic inflammation and differentiate into plasma cells that produce antibodies, though the exact role of antibodies is not fully understood in this context.
• 😀 Chronic inflammation can result in the formation of tertiary lymphoid organs, which are clusters of immune cells at the site of inflammation (e.g., seen in chronic autoimmune diseases).
• 😀 Other important cells in chronic inflammation include eosinophils (in parasitic infections), mast cells (in both acute and chronic inflammation), and neutrophils (which can persist in chronic conditions).

Q & A

What is chronic inflammation, and how does it differ from acute inflammation?

Chronic inflammation is a prolonged response that can last weeks to months, unlike acute inflammation, which is an immediate response lasting days. Chronic inflammation involves inflammation, tissue injury, and attempts at repair, all coexisting in varying combinations.

What are the main causes of chronic inflammation?

Chronic inflammation can occur due to persistent infections, hypersensitivity diseases (such as autoimmune disorders), and prolonged exposure to toxic agents, including both exogenous (e.g., silica) and endogenous (e.g., cholesterol) substances.

Can chronic inflammation occur without prior acute inflammation?

Yes, chronic inflammation may or may not follow from acute inflammation. It can develop independently, for example, due to persistent infections or autoimmune diseases.

How does cholesterol contribute to chronic inflammation?

Excessive cholesterol can lead to conditions like atherosclerosis, where inflammation becomes a predominant feature, contributing to tissue injury and the development of chronic inflammation.

What are the morphological features of chronic inflammation?

Chronic inflammation is characterized by infiltration of mononuclear cells (macrophages, lymphocytes, plasma cells), tissue injury, and repair attempts such as angiogenesis (proliferation of blood vessels) and fibrosis (scar tissue formation).

What role do lymphocytes play in chronic inflammation?

Lymphocytes, particularly CD4+ T cells and B cells, play a key role in chronic inflammation. CD4+ T cells promote inflammation through various subtypes (e.g., Th1, Th2, Th17), while B cells produce antibodies that may contribute to the persistence of inflammation.

What is the function of CD4+ T cells in chronic inflammation?

CD4+ T cells, or T helper cells, secrete cytokines like interferon-gamma (Th1), interleukins (Th2), and interleukin-17 (Th17), which activate macrophages and other immune cells, driving inflammation and tissue damage.

What are tertiary lymphoid organs, and how do they relate to chronic inflammation?

Tertiary lymphoid organs are clusters of immune cells (including T cells, B cells, and plasma cells) that form at sites of chronic inflammation, such as in Hashimoto's thyroiditis or chronic pyelonephritis. Their significance in chronic inflammation is not yet fully understood.

How do eosinophils contribute to chronic inflammation?

Eosinophils are involved in immune reactions mediated by IgE, especially in parasitic infections. They release toxic proteins that damage both the invading pathogens and the host’s epithelial cells, exacerbating tissue injury in chronic inflammation.

Can neutrophils be found in chronic inflammation, and if so, why?

Yes, neutrophils can be present in chronic inflammation, particularly when microbial agents persist and are not eradicated. Neutrophils help contain the infection, but their presence may also contribute to further tissue damage.