Neutrophils

Tags:

No items found.

Immunology

Summary

Neutrophils are a vital component of our immune system, constituting approximately 70% of all circulating white blood cells. Known for their rapid and effective response to infections or injuries, neutrophils are often referred to as the 'first responders' of the immune system. Their primary function is to exterminate infectious agents through a process known as phagocytosis Neutrophils undergo a multi-step migration process from the bloodstream to the site of infection or injury. Their journey begins at the inciting injury, where macrophages recognize invaders and secrete cytokines such as TNF and IL-1. These cytokines trigger endothelial cells to express selectins and neutrophils to express low-affinity state integrin, or selectin ligands(SLIG). The binding of selectins to SLIG have low-affinity adhesions, resulting in deceleration and 'rolling' of the migrating neutrophils, allowing them to respond to additional signals such as strong>C5a and lipopolysaccharide (LPS) as they continue their journey toward the site of injury. These signals trigger the neutrophils to express high-affinity state integrin (ex. CD18), which bind to ICAM-1 on endothelial cells, resulting in firm adhesion and the neutrophils 'crawling' along the endothelial wall. Neutrophils exit the bloodstream via transmigration, a process mediated by PECAM-1, an adhesion molecule primarily expressed at the junctions of adjacent endothelial cells. Using PECAM-1, neutrophils squeeze out of the vascular space, assisted by chemokines released at the site of injury like IL-8 that induce the chemotaxis of the neutrophil to the infection site and stimulates phagocytosis of the invading pathogens. In addition to their role as phagocytes, neutrophils secrete chemotactic cytokines like TNF, as well as antimicrobial granules, and neutrophil extracellular traps (NETs) to neutralize invading pathogens. In fact, neutrophils work so hard to protect us, that dead neutrophils accumulate and make up the majority of what we see as pus.

Lesson Outline

Don't stop here!

Get access to 22 more Immunology lessons & 13 more medical school learning courses with one subscription!

Try 7 Days Free

FAQs

What is the role of MHC 1 and MHC 2 in antigen processing and presentation to T-cells?

Both MHC class one (MHC 1) and MHC class two (MHC 2) are essential for antigen processing and their presentation to T-cells. MHC 1 typically presents endogenous proteins (those produced within a cell) to CD8+ T-cells, while MHC 2 presents exogenous proteins (those from outside the cell) to CD4+ T-cells. These processes are vital for immune response initiation.

What is the difference between the MHC I pathway and the MHC II pathway in the context of antigen processing?

The MHC I pathway processes and presents endogenous proteins. It involves the degradation of these proteins by proteasomes into peptides, which then bind to MHC 1 molecules and are presented to CD8+ T-cells. On the contrary, the MHC II pathway deals with exogenous proteins. These proteins are internalized into endosomes, where they are degraded. The resulting peptides are bound by MHC 2 molecules, which are then presented to CD4+ T-cells.

What are the roles of the Invariant chain and HLA-DM in the MHC II pathway?

The Invariant chain plays a crucial role in MHC II assembly and transport. It associates with the MHC II molecule in the endoplasmic reticulum, preventing premature binding of peptides. The Invariant chain also guides MHC II to endosomal compartments, where it is degraded. HLA-DM then helps to remove the remaining Invariant chain fragments and facilitates the binding of the processed exogenous antigen peptides to the MHC II molecule for presentation to T-cells.

How does the antigen presentation process direct the immune response?

Antigen presentation is crucial in determining the type of immune response. If an antigenic peptide is presented by MHC 1 molecules, it activates CD8+ T-cells, leading to a cytotoxic response and the killing of infected cells. If the peptide is presented by MHC 2 molecules, it activates CD4+ T-cells, leading to a helper response that can stimulate B cells to produce antibodies or macrophages to kill ingested microbes.

How do MHC-peptide complex variations influence antigen processing and presentation to T-cells?

The variation in MHC-peptide complexes impacts the specificity of antigen recognition. Each individual has many different MHC molecules that can bind and present different peptides. The unique combination of MHC molecules and their bound peptides determines the assortment of T-cells activated during an immune response. These variations are key to the versatility and specificity of the adaptive immune response.

MCAT® is a registered trademark of the Association of American Medical Colleges. The United States Medical Licensing Examination (USMLE®) is a joint program of the Federation of State Medical Boards (FSMB®) and National Board of Medical Examiners (NBME®). NAPLEX® is a registered trademark of the National Association of Boards of Pharmacy. PANCE© is a registered trademark of the National Commission on Certification of Physician Assistants. NCLEX® is a registered trademark and service mark of the National Council of State Boards of Nursing, Inc. None of the trademark holders are endorsed by nor affiliated with Sketchy or this website.