Chronic Inflammation - Introduction

Introduction

• Chronic inflammation may:
  • Follow on from an unresolved acute inflammation.
  • Be chronic from the beginning.
    • Is usually of slow onset and long duration, and very insidious in nature.
    • There is a slow progressive destruction of the original tissue.
• Chronic inflammation is characterised by cellular infiltration and proliferation of local connective tissue.
  • Often found around focal areas of necrosis.

Cells

• The principal inflammatory cells involved are lymphocytes and macrophages.
  • Fibroblasts and vascular endothelium also have important roles.

Accumulation of Macrophages

• Under certain circumstances, macrophages accumulate.
  1. Impaired digestive ability of the macrophages to cope with foreign material.
     • E.g. thorns, sutures, grit etc.
  2. The irritant being able to coat itself with host antigens.
     • E.g. Actinobacillus bacteria form enveloping 'clubs'.
  3. The irritant's own coating being impervious to digestion by the macrophage.
     • E.g. tubercle bacillus and fungi.

Fibroblasts

• Derived from local connective tissue cells.
• Involved in the organisation of damaged tissue.
  • Replacement repair.

Endothelium

• As well as fibroplasia (organisation) and macrophages mopping up debris, the vascular endothelium proliferates into the organising tissue.
• Endothelium is a prominent component of the 'pyogenic membrane’ in abscess formation.
  • The vessels bring neutrophils into the centre of the abscess.