Chronic Inflammation

Inflammatory Cells

Macrophages

Macrophages are the major phagocytic cell in chronic inflammation, acting to engulf and destroy foreign material and/or pathogens, and are derived from monocytes.

Macrophages also act as antigen presenting cells (APCs), whereby antigens are presented from the innate immune cells to the adaptive immune cells. This process allows for a more coordinated and targeted response from the immune system in chronic inflammation. They also secrete growth factors and cytokines, to help coordinate the immune response.

Macrophages can also fuse and form multi-nucleated giant cells (Fig. 1) in chronic inflammation. They are produced in response to certain stimuli, such as a foreign body (foreign-body giant cell), mycobacterium tuberculosis (Langhans giant cell), or fat necrosis (Touton giant cell).

By Nephron (Own work) [CC BY-SA 3.0], via Wikimedia Commons

Figure 1
Multinucleated giant cells, formed by the fusion of macrophages

Lymphocytes

In chronic inflammation, lymphocytes work in conjunction with APCs to process antigens, thereby coordinating a suitable inflammatory response. There are two main types, B lymphocytes and T lymphocytes (Fig. 2).

B Lymphocytes

When appropriately stimulated, B lymphocytes differentiate into plasma cells. Plasma cells are essential for antibody production, which are used for:

• Neutralising microbes and toxins (binding to and blocking the harmful effects of the antigen), to prevent infective and toxic effects of the antigen
• Promote natural killer cells to destroy targeted and tagged pathogens (termed antibody dependant cellular cytotoxicity, or ADCC)
• Facilitate easier phagocytosis by the innate immune cells (termed opsonisation)

T Lymphocytes

T helper lymphocytes (CD4+ cells) act to co-ordinate further targeted inflammatory responses, from both innate and adaptive immune cells. T killer lymphocytes (CD8+ cells) act to co-ordinate the targeted destruction of infected cells.

By TeachMeSeries Ltd (2026)

Figure 2
The roles of B lymphocytes (left) and T lymphocytes (right) in chronic inflammation

Granulomas

In chronic inflammation, macrophages and lymphocytes can combine to form a granuloma (Fig. 3), a means by which the immune system can “wall off” an agent particularly resistant to destruction.

A granuloma contains a collection of elongated macrophages, termed epithelioid cells, surrounding a core of lymphocytes and giant cells attempting to break down the particles.

They are observed in several disease states, such as tuberculosis, sarcoidosis, Crohn’s disease, Rheumatoid arthritis, and Granulomatosis with polyangiitis (GPA).

As granulomatous inflammation progresses, fibroblasts begin to lay down scar tissue, whilst the central core can become necrotic due to the release of enzymes (particularly seen in tuberculosis).

By Yale Rosen [CC BY-SA 2.0], via Wikimedia Commons

Figure 3
A granuloma in sarcoidosis, showing a central core of lymphocytes surrounding by macrophages