Microbiology Exam 3 - Biological Mechanisms of Defense

what are the general functions of innate immune first-line defenses?

all first-line defenses assist in preventing pathogen entry and respond to invaders through attacking any organisms that do not belong in the body

mechanical barriers

flush or trap pathogens to limit the spread of them

examples of mechanical barriers

tears, mucus, cilia

chemical barriers

can directly attack the pathogen or make the environment uninhabitable for pathogen survival in or on a specific body tissue

examples of chemical barriers

stomach acid, saliva, antimicrobial peptides

physical barriers

structures that physically block pathogen entry into the body

examples of physical barriers

epithelial tissue, epidermis

lysozyme

an enzyme that acts as a part of the first-line of defense and a chemical barrier and helps protect the body by breaking down bacterial cell walls which allows it to directly attack invaders

where are lysozymes found?

in mucus, saliva, tears, which are secretions rich in substances that serve as chemical barriers

antimicrobial peptides

first line of defense chemical barrier that get released by neutrophils. once released into the environment, breakdown microbes such as bacteria, fungi, viruses, and parasites

defensin

specific type of AMP found in mammals. they kill the pathogen by inserting themselves in the cell membrane of the invader and poke holes in membranes by embedding themselves in them – causes them to lose their function and microbial cell dies

two categories of second-line defenses

cellular defenses and molecular defenses

cellular defenses

granulocytes and agranulocytes

molecular defenses

cytokines, iron-binding proteins, complement proteins

lymph

fluid that comes from blood plasma. While blood is being delivered to the tissues, some plasma will leak out of the capillaries and seep into interstitial fluid between tissue cells. When lymphatic capillaries take up interstitial fluid to return it to our bloodstream, the fluid is then called lymph

lymph collection/filtration

1. Plasma exits capillaries into the space between cells and is renamed to interstitial fluid

2. Interstitial fluid from the tissues is then collected by lymph capillaries and when it enters these lymphatic vessels, it is renamed to lymph

3. After being filtered at a lymph node, lymph rejoins blood via veins and is again plasma

leukocytes

white blood cells are responsible for protecting your body from infection. As part of your immune system white blood cells circulate in your blood and respond to injury and illness

main types of leukocytes

granulocytes and agranulocytes

granulocytes

contain large visible cytoplasmic granules and usually have lobed nuclei. they function in innate immunity and generally have a shorter life span of a few hours or days

main types of granulocytes

neutrophils, eosinophils, basophils

agranulocytes

do not have prominent visible granules and have more regular non-lobed nuclei. primarily function in adaptive immunity and some can live for years

type main types of agranulocytes

lymphocytes and monocytes

structural features of granulocytes

form in bone marrow then enter the bloodstream and typically range form 1,500-8,500 cells per microliter of blood

neutrophils

attack bacterial and fungal infections, most abundant granulocyte; highly phagocytic, adherent, and motile; and acts as a first line of defense against pathogens being recruited to inflammatory cites

eosinophils

shows up with immune response (ex: allergies)

basophils

release histamine and heparin (when allergic reactions occur), work alongside mast cells and produce cytokines to defend against parasites along with allergic reaction

histamine

removes allergens

heparin

blood thinner, prevents clotting

mast cells

remain in specific tissues, similar to basophils structurally but these have longer life spans and do not rush to inflammation spots

functional features of granulocytes

during inflammation, these rush to the area and release granules to fight off and get rid of the infection

monocytes

a type of WBC whose levels increase as a result of infection, inflammation, autoimmune disorders, and certain cancers

what do monocytes mature into? when does this happen?

macrophages as they migrate out of the circulatory system into tissues

macrophages

highly phagocytic, pathogen destroying cells; types are fixed and wandering

fixed macrophages

tissue-specific in where they reside

wandering macrophages

roam through tissues

dendritic cells

highly phagocytic leukocytes residing in tissues frequently in contact with the environment. they function as antigen-presenting cells that prevent immune response among non-threatening substances and self-antigens

what are dendritic cells named after?

named for long cytoplasmic extensions called dendrites which increase surface area

natural killer cells

type of lymphocyte that plays an important role in innate immunity, directly killing virus-infected cells and tumor cells, also protecting against bacteria and parasites; play a role in adaptive immunity but lack antigen-specific cell surface receptors

where are NKT cells abundant?

in the liver

three main pathways for complement activation

classical pathway, lectin pathway, alternative pathway

classical pathway

triggered by antibodies bound to a pathogen

lectin pathway

triggered by lectin proteins binding to carbohydrates on pathogen surfaces (antibodies NOT required)

classical, lectin, and alternative pathway outcomes

inflammation, opsonization, and cell lysis

alternative pathway

triggered by direct contact of complement proteins with pathogen surfaces

cytokine functions

• stimulate inflammation

• generate fever

• recruit leukocytes to fight infection

• stimulate tissue and blood vessel repair

• promote leukocyte and lymphatic tissue development

• antiviral effects

• immune system regulation/activation

4 categories of cytokines

interferons, chemokines, tumor necrosis, interleukins

interferons*

Interferon-alpha and Interferon-beta both made virus-infected cells signal neighboring cells to mount antiviral defenses; immune responses to viruses, bacteria, and parasites; Interferon- alpha can also trigger fever

chemokines

recruit white blood cells to areas of injury or infection, wound healing, blood vessel formation, repair, lymphoid tissue development

tumor necrosis factors

mainly made by macrophages, induce inflammation, kill tumor cells, and can also induce fever

interleukins

regulate inflammation and generate fever, influence T cell development, and generate the immune system’s self-tolerance

acute phase

occurs immediately after injury or infection

acute phase process

immune system sends inflammatory cells to affected area, increased blood flow causes redness, warmth, swelling, and pain. this phase helps contain the damage and start the healing process

cellular/defensive phase

WBCs and inflammatory chemicals continue working at the site by trapping and destroying pathogens, removing toxins, and clearing damaged tissues. swelling and tenderness may continue as immune cells work to eliminate the threat

resolution/healing phase

once the threat is eliminated, inflammation decreases and the body repairs damaged tissues to restore normal function. if inflammation does not resolve properly, it can become chronic inflammation lasting months to years and damaging tissues

chronic inflammation

your body continues sending inflammatory cells even when there is no danger - sometimes it improves, sometimes it gets worse

fever

abnormally high body temperature (100.4+ degrees F)that is a systemic response to invading microorganisms

fever benefits

causes liver and spleen to sequester iron and zinc, which is needed by microorganisms to cause infection - this causes increased metabolic rate and increased rate of repair, increased body temp also inhibits microbes from multiplying

antigen

any molecule that can trigger an immune response in the body

where can antigens come from?

pathogens, allergens, or transplanted tissue or foreign cell

epitope

the specific part of an antigen that isactually recognized and bound by an antibody or a receptor on a T cell

antigen and epitope relationship

one antigen can have multiple epitopes, meaning it can be recognized by different antibodies

where do T cells mature?

in the thymus

where do B cells mature?

in the bone marrow

how do T cells recognize antigens?

recognize on MHC molecules

how do B cells recognize antigens?

recognize free antigens directly

T cell role

help coordinate immunity and can kill infected cells

B cell role

differentiate into plasma cells that make antibodies

T cells form ___

memory __ cells for future protection

B cells form ___

memory ___ cells for long-term immunity

4 cellular adaptive immune response stages

1. antigen presentation

2. lymphocyte activation

3. lymphocyte proliferation and differentiation

4. antigen elimination and memory

stage 1: antigen presentation

antigen-presenting cells use major histocompatibiliy complexes (MHCs) 1 or 2 to present antigens to T cells

stage 1: antigen presentation (humoral)

B cells act as antigen-presenting cells, so they don’t require another antigen-presenting cell to process and present antigens - instead, they have two different paths to activation; the route taken depends on the type of antigen

MHC 1

presenting intracellular antigens to T cytotoxic cell

MHC 2

presenting extracellular antigens to T helper cells

stage 2: lymphocyte activation

T cells are activated by antigen-presenting cells in lymphatic tissues

stage 2: lymphocyte activation (humoral)

B cells are activated by T-dependent and T-independent antigens

stage 3: lymphocyte proliferation and differentiation

activated T cells undergo proliferation and differentiation

stage 3: lymphocyte proliferation and differentiation (humoral)

activated B cells proliferate and differentiate into plasma cells and memory cells

stage 4: antigen elimination and memory

effector T cells eliminate antigens and memory T cells remain in lymphatic tissue

stage 4: antigen elimination and memory (humoral)

plasma cells secrete antibodies that bind to the antigen that triggered the B cell’s activation - three key antibody functions help eliminate antigens

functional features of antibodies

neutralizes antigens, activates complement, increases phagocytosis

neutralizing antigens

antibodies block toxins or antigens from binding to host cells

activate complement

complement activation leads to cytolysis, opsonization, inflammation

increased phagocytosis

phagocytosis is enhanced as antibodies agglutinate, precipitate, and opsonize antigens

five classes of immunoglobulins (antibodies)

IgG, IgA, IgM, IgE, IgD

IgG

half-life of 21 days, crosses the placenta is is made later in infections

IgA

half-life of 6 days and is a main antibody in breast milk, and is resistant to destruction by stomach acid

IgM

half life of 10 days and is made early in infection and is a large structure that limits where it migrates

IgE

half life of 2 days, fights parasites, and mediates allergic responses

IgD

half life of 2 days, is bound to B cells and is poorly understood

together the innate and adaptive systems

distinguish self from foreign, kill invaders, and are effective against diverse threats, and function as an integrated, bidirectional network with rapid, non-specific innate responses that initiate and shapes the specific, long-term adaptive response