Immunology Innate Immunity

9/3/2025

Inflammation: phagocyte recruitment

Dendritic cells, macrophages and others secrete Tumor Necrosis Factor (TNF) and IL-1. TNF and IL-1 in turn then increase expression of adhesion molecule, E-selectin on venular endothelial cells. This help connect cells and get things where they need to go. Surface carbs on neutrophils and monocytes bind to selectins. Blood flow dislodges leukocytes temporarily before they bind again through the process of rolling.

What does rolling do for inflammation?

Rolling leukocytes encounter chemokines produced by macrophages and endothelial cells. Chemokines bind to these rolling leukocytes which causes a high expression of integrins, which stops them from looping and rolling. The cytoskeleton will then change and spread over the endothelial surface. The leukocytes (as a flat pancake) now can get into the body’s tissues.

The gradient is…

Highest near the invading bacteria, leading leukocytes to it.

Microbe destruction after being phagocytized

Microbially-derived ligands, and ligands on opsonized microbes initiate internalization. The plasma membrane extends and is pinched off and is turned into a phagosome. Phagosome gets to lysosome for enzymes to kill microbe via reactive oxygen species (ROS) or (iNOS) with nitric oxide synthase. Lysosomal proteases break down the microbial proteins. Neutrophils also produce granules to kill extracellular microbes.

Phagocytosis is…

when particles are larger than 0.5 um are consumed.

Neutrophil

Uses more ROS

Antiviral Defense

Type I interferons (IFNs) are secreted by infected cells when they detect viral nucleic acid by TRLs and other PRRs. Type I IFNs bind to receptors on infected and non-infected cells to inhibit viral replication. Infected cells are destroyed by NK cells via recognizing lack of MHC and when the quality check fails, it kills the cell.

Stimulating Adaptive Immunity

Antigen-specific lymphocytes need two signals: 1. Antigen and 2. Innate immune responses to microbes and host cell damage-ensures that they are being stimulated by more than one signal and realize they need to expand and separate and differentiate. Co stimulates T cell and B cell production.