TRANSIENT CELLS OF THE CONNECTIVE TISSUE – 2
Inflammatory infiltrate
The connective tissue is the main site of inflammatory reactions in the body.
The number of transient cells increases significantly when there is local inflammation. In this case, chemical signals emitted by dead microorganisms and local cells, mainly macrophages, neutrophils, and eosinophils, attract leukocytes to this region. A large number of leukocytes accumulated at a site of an inflammatory response is called an inflammatory infiltrate.
The types of cells present in an inflammatory infiltrate vary greatly, depending mainly on:
1 – The agent that initially provoked this reaction. The cell population can be very different depending on whether the reaction is against a bacterium, a protozoan, or a physical agent (e.g., heat radiation, i.e., a burn).
2 – The moment when the inflammatory reaction is observed. For example, after a bacterial infection, there is initially an immediate, acute response, consisting primarily of neutrophils and perhaps eosinophils. In a later phase, many lymphocytes and plasma cells appear, as well as macrophages. Later, only these latter cells may persist, without the presence of neutrophils and eosinophils.
The number of transient cells increases significantly when there is local inflammation. In this case, chemical signals emitted by dead microorganisms and local cells, mainly macrophages, neutrophils, and eosinophils, attract leukocytes to this region. A large number of leukocytes accumulated at a site of an inflammatory response is called an inflammatory infiltrate.
The types of cells present in an inflammatory infiltrate vary greatly, depending mainly on:
1 – The agent that initially provoked this reaction. The cell population can be very different depending on whether the reaction is against a bacterium, a protozoan, or a physical agent (e.g., heat radiation, i.e., a burn).
2 – The moment when the inflammatory reaction is observed. For example, after a bacterial infection, there is initially an immediate, acute response, consisting primarily of neutrophils and perhaps eosinophils. In a later phase, many lymphocytes and plasma cells appear, as well as macrophages. Later, only these latter cells may persist, without the presence of neutrophils and eosinophils.
The image shows an area of connective tissue beneath a stratified squamous epithelium. Observe in this connective tissue a large accumulation of cells that, upon higher magnification, are found to be leukocytes. This is the type of localized and abnormal accumulation of leukocytes called an inflammatory infiltrate. Inflammatory infiltrates are very educational sites for observing the transient cells of connective tissue, which will be discussed in the following pages of this series.
Inflammatory infiltrate. Staining: HE. Magnification: low.
