Innate immunity is our body's first line of defense, acting fast to protect us from invaders. It's like a security system that's always on, using physical barriers, chemicals, and special cells to keep us safe.

Our skin and mucous membranes are like fortress walls, while stomach acid and enzymes act as chemical weapons. When trouble strikes, inflammation kicks in, calling for backup and starting the healing process.

Physical and Chemical Barriers

Characteristics of innate immunity

• Innate immunity forms first line of defense against pathogens present from birth providing non-specific response to invaders
• Key characteristics include rapid response within minutes to hours no immunological memory and evolutionarily conserved mechanisms across species
• Components encompass physical barriers (skin, mucous membranes) chemical barriers (acids, enzymes) cellular components (neutrophils, macrophages) and humoral components (complement proteins)

Physical and chemical immune barriers

• Physical barriers include skin with stratified squamous epithelium and keratin layer mucous membranes lining respiratory gastrointestinal and urogenital tracts and cilia in respiratory tract trapping particles
• Chemical barriers comprise low pH and antimicrobial sebum on skin surface mucus trapping pathogens and containing antimicrobial proteins stomach acid (HCl) enzymes like lysozyme in tears and saliva pepsin in stomach and antimicrobial peptides (defensins, cathelicidins)

Role of inflammation in immunity

• Inflammation triggered by tissue damage or pathogen detection characterized by cardinal signs (redness, heat, swelling, pain)
• Vascular changes involve vasodilation increased blood flow and vascular permeability
• Cellular responses include neutrophil recruitment and macrophage activation
• Chemical mediators released histamine prostaglandins leukotrienes and cytokines
• Functions encompass pathogen containment tissue repair initiation and adaptive immune system activation

Complement system in innate defense

• Complement system network of plasma proteins activated in cascade manner through classical alternative or lectin pathways
• Functions include opsonization of pathogens chemotaxis of immune cells and formation of membrane attack complex (MAC)
• Key complement proteins C3 C5 and Factor B play crucial roles in cascade
• Regulation by complement regulatory proteins prevents host tissue damage
• Complement deficiencies lead to increased susceptibility to infections and autoimmune disorders (systemic lupus erythematosus)