Which of the following composes majority of the leukocyte infiltrate after the first 24 hours of inflammatory response?
**Core Concept**
The inflammatory response is a complex process involving the coordinated action of various cell types and chemical mediators. After the initial 24 hours, the composition of the leukocyte infiltrate changes, with certain cell types becoming predominant.
**Why the Correct Answer is Right**
The majority of the leukocyte infiltrate after the first 24 hours of inflammatory response is composed of **macrophages**. These cells are derived from circulating monocytes that migrate to the site of inflammation in response to chemokines and other inflammatory mediators. Macrophages play a crucial role in the resolution of inflammation by phagocytosing pathogens, dead cells, and debris, and by producing anti-inflammatory cytokines that help to reduce the intensity of the inflammatory response. The production of **tumor necrosis factor-alpha (TNF-alpha)** and **interleukin-1 (IL-1)** by macrophages also contributes to the maintenance of the inflammatory response.
**Why Each Wrong Option is Incorrect**
**Option A:** **Neutrophils** are the predominant leukocyte type during the acute phase of inflammation (0-24 hours), but they are not the majority after the first 24 hours.
**Option B:** **Lymphocytes** are present in the inflammatory infiltrate, but they are not the majority after the first 24 hours. Lymphocytes play a key role in the adaptive immune response, which is a delayed response to inflammation.
**Option C:** **Eosinophils** are not typically involved in the acute inflammatory response and are not the majority after the first 24 hours. Eosinophils are more commonly associated with allergic reactions and parasitic infections.
**Clinical Pearl / High-Yield Fact**
After the first 24 hours of inflammation, the leukocyte infiltrate shifts from a predominantly neutrophilic response to a macrophage-dominated response, which is critical for the resolution of inflammation and the restoration of tissue homeostasis.
**Correct Answer:** C. Macrophages.