Immunity—non-specific/innate

• Overview of immune response• First line of defense—barriers• Second line of defense

– Phagocytosis– Inflammation– Complement– Fever

• Relationship to specific immune response or Third line of defense

Immune Response—Overview

First Line of Defense

• Physical barrier on all surfaces of body exposed to external world

• What are they?– Skin– Mucous membranes—nasal, respiratory– Lining of mouth– Lining of gut– Lining of vagina/urethra– Surface of eye

Barrier Membranes

Skin

How do barrier membranes keep bacteria out?

• Chemical barrier—antibacterial secretions• Cellular barrier—cells tightly packed and

sloughed off (10B skin cells/day=250 g./year)• Physical barrier—thick, mucousy and sticky

secretions trap bacteria• Resident microbes—have commensal or

mutualistic bacteria and fungi that are normally present and out-compete potential pathogens

• First line of Defense—physical barrier

• Second Line of Defense– Phagocytosis– Inflammation– Complement– Fever– All work tightly with specific immunity

• Phagocytes move through blood and lymph and into connective tissues (part of inflammation response as cells and fluid move out of capillaries into surround aleolar tissues--diapedesis)

Phagocytosis

•Langerhans cells in skin•Phagocytes in blood•Microglial cells in CNS

Complement

• Group of free proteins in blood that respond to antigen/antibody complex (huh?—coming soon)

• Cascade of reactions eventually makes MAC’s—membrane attack complex—that bores hole in bacterial membrane

• Gram-negative bacteria more susceptible

Inflammation• Response to tissue damage from any

source (burn, cut, pathogen, other??)• Blood vessels dilate allowing for better

delivery of nutrients, O2, antibodies, complement, immune cells

• Phagocytes (monocytes and neutrophils) migrate out of capillaries--diapedesis

Fever

Pluses• Inhibit microbial growth• Enhance immune cell

performance• Speed tissue repair

Minuses• Malaise• Body aches• chills

Trigger not completely understoodMuscular contraction and constriction of skin blood vessels cause core temperature to rise

“Breaking” fever or “crisis of fever”: • body begins to cool by sweating,• “color returns” as blood vessels in skin open• Indicates infection is overcome

Links from innate (2nd line) to specific/adaptive (3rd line) Immunity

• Phagocytosis continues to be common way to kill pathogenic cells in both specific and non-specific response

• Inflammation works to allow both specific and non-specific immune response to accelerate

• Fever also allows for better performance in both specific and non-specific function

• Specific immune response and “antigen presentation” further stimulates non-specific actions like phagocytosis, complement.

Links from innate (2nd line) to specific/adaptive (3rd line) Immunity