Chapter 1: Innate Immunity

Study Notes

Barriers

Skin consists of the epidermis and dermis; epidermis has several layers of tightly bound epithelial cells, mainly dead cells and keratin, providing impermeability.
Mucous membranes line the respiratory, gastrointestinal, and urogenital tracts, serving as barriers against outside pathogens; mucus traps pathogens, cilia expel microorganisms, and saliva contains antimicrobial components.
Scratches, insect bites, and wounds serve as entry routes for microbes, leading to potential infections.
Active biochemical defenses include peptides and proteins like Psoriasin, which has potent antimicrobial activity against E. coli.

Competition

Pathogenic microorganisms must compete with normal flora for binding to epithelial cells and access to nutrients.

Pathogen Evasion

Pathogen binding to mucous membranes can determine the level of invasion, such as the influenza virus's ability to adhere strongly to respiratory mucosal surfaces, hindering elimination.

Systems of Pathogens' Perception

Infections result from pathogens crossing anatomical and physiological barriers, triggering the immune response that includes detection and destruction functions.
Detection occurs through interactions between pathogens and host membranes or soluble molecules—differentiating self from non-self.

Molecular Signatures

Pathogen-associated molecular patterns (PAMPs) are molecular signatures on microbes, such as peptidoglycan from Gram-positive bacteria and lipopolysaccharide (LPS) from Gram-negative bacteria.
PAMPs are invariant, not found in the host, and are shared by large groups of pathogens.

Pattern Recognition Receptors (PRRs)

Toll-Like Receptors (TLRs) recognize specific PAMPs. For instance, TLR-2 recognizes proteoglycans of Gram-positive bacteria, while TLR-4 recognizes LPS from Gram-negative bacteria.

TLR-4 and LPS Interaction

LPS, an endotoxin from Gram-negative bacteria's outer membrane, is linked to septic shock; TLR-4 is a receptor for LPS, part of a complex that includes CD14, a phagocytic cell marker.
LPS binds to a soluble protein known as LPS binding protein (LBP), which then binds to CD14, activating phagocytes through interactions with TLR-4 and transcription factor NFκB.

Humoral Factors

Immune responses include humoral factors like immunoglobulins (Ig) and fragments of activated complement; pathogens possess receptors for the Fc portion of Ig and specific complement fragments (CR1, CR3).

Immune Actors

Key immune cells: phagocytes (monocytes, macrophages, neutrophils, dendritic cells) and Natural Killer (NK) cells are essential in responding to pathogens.
Role of B cells in phagocytosis will be discussed later.

Hematopoiesis

Pluripotent cells are foundational for hematopoiesis, possessing self-renewal and differentiation capacities, critical for immune cell generation.

Description

This quiz focuses on the key concepts of innate immunity covered in Chapter 1. It explores various barriers, including skin and mucous membranes, their structure, and their roles in the immune system. Test your understanding of the actors and modes of action involved in innate immunity.