Extravasation follows a precise multi-step adhesion cascade. First, endothelial P- and E-selectins grab passing neutrophils and cause them to roll slowly along the vessel wall. Rolling neutrophils then encounter chemokines displayed on the endothelial surface, triggering conformational activation of integrins from low-affinity to high-affinity state — causing firm arrest. The firmly arrested neutrophil then squeezes between endothelial cells (diapedesis) and follows the chemokine gradient into infected tissue. Each step is necessary: blocking selectins prevents rolling and eliminates all downstream steps.
Question 2 Multiple Choice
During acute inflammation, fluid leaks out of blood vessels into tissue, causing swelling (edema). Which of the following best describes the functional role of this edema?
AEdema is purely a harmful side effect that the body attempts to minimize; its only purpose is to signal pain
BEdema delivers plasma containing complement proteins and antibodies into the infected tissue, providing additional antimicrobial defense
CEdema dilutes toxins produced by pathogens, reducing their local concentration
DEdema creates physical pressure that mechanically traps pathogens in the infected zone
Increased vascular permeability is not collateral damage — it is functional. The leaked plasma carries soluble immune components: complement proteins (which can directly kill bacteria, coat them for phagocytosis, and recruit more immune cells) and antibodies. These components reach the infected tissue through the same gaps in the endothelium that neutrophils will later use for diapedesis. The swelling is thus both a consequence and a contributor to the antimicrobial response. This is why anti-inflammatory drugs that reduce edema can, if used excessively early in infection, impair the immune response.
Question 3 True / False
Neutrophils arrive at sites of infection before monocytes because neutrophils are the first white blood cells recruited through the leukocyte extravasation cascade during acute inflammation.
TTrue
FFalse
Answer: True
Neutrophils are the first responders in acute inflammation, arriving within minutes to hours of the initial alarm signals. They are abundant in blood, express the selectin ligands and integrins needed for the adhesion cascade, and respond rapidly to the first wave of chemokines. Monocytes arrive later — typically over the next day or two — and differentiate into macrophages in the tissue. The sequential arrival reflects different sensitivities to chemokine signals and different adhesion molecule profiles. This temporal pattern means neutrophil-dominated inflammation characterizes early acute infection, while macrophage-dominated inflammation characterizes later phases and chronic infection.
Question 4 True / False
The inflammatory response is self-perpetuating once started and is expected to be suppressed by the adaptive immune system to resolve.
TTrue
FFalse
Answer: False
Inflammation is self-limiting through intrinsic mechanisms that operate in parallel with pathogen clearance. As pathogens are eliminated, the pro-inflammatory cytokine stimulus diminishes. Anti-inflammatory cytokines like IL-10 and TGF-β shift the cytokine balance toward resolution. Macrophages switch from pro-inflammatory (M1) to tissue-repair (M2) phenotypes. These mechanisms are innate, not dependent on adaptive immunity — though adaptive immunity can accelerate and amplify both the inflammatory and resolution phases. Chronic inflammation occurs precisely when these self-limiting mechanisms fail, leading to persistent tissue damage in conditions like rheumatoid arthritis.
Question 5 Short Answer
How does the cellular inflammatory response bridge innate and adaptive immunity?
Think about your answer, then reveal below.
Model answer: Dendritic cells at the site of inflammation capture antigens from pathogens and, upon activation, undergo a maturation process that increases their antigen-presenting capacity and upregulates co-stimulatory molecules. They then migrate through lymphatic vessels to draining lymph nodes, where they present processed peptide fragments on MHC molecules to naïve T cells. This antigen presentation, combined with co-stimulatory signals and cytokines produced during the innate response, activates antigen-specific T cells to proliferate and differentiate — initiating the adaptive immune response. The innate inflammatory response thus provides both the antigen (via dendritic cell capture) and the co-stimulatory signals (via pattern recognition receptor activation) that are required for adaptive immunity to begin.
The dendritic cell is the key bridge cell. Without the inflammatory context provided by the innate response — particularly the danger signals detected by toll-like receptors and the cytokines produced by macrophages — dendritic cell maturation is incomplete, and naïve T cells encountering antigen without co-stimulation become anergic (tolerant) rather than activated. This is why adaptive immunity is activated by infection but tolerates self-tissues: self-antigens are typically presented in the absence of inflammatory danger signals.