Microbiology Exam 3 Study Guide

immune system

protects the body against pathogenic microbes

recognizes our cells as “self” and doesn’t destroy them

innate vs. adaptive immune response

innate: some immune cells exhibit antimicrobial function immediately after infection and in the same way during re-infection, every time (same every time)

adaptive: other immune cells exhibit antimicrobial function after infection more slowly, but in a more protective, longer-lasting way (faster, better, stronger)

pathogen

microbe that causes disease in its host

infection vs. disease

infection: when a microbe invades the body + multiplies

disease: tissue damage due to infection

pathogenesis

molecular and cellular events that cause tissue damage and disease

pathogenecity

ability of a microbe to cause disease in a host; defined by both the microbe and the immune response

damage-response framework

adequate: sweet spot; enough immune response to take care of the pathogen but not so much that you damage yourself

too little immune response → pathogen causes tissue damage

too much immune response → immune response causes tissue damage

5 characteristics that make a pathogen successful

ability to…

1) colonize the host (attachment and entry)

2) find a nutritionally compatible niche in the host

3) avoid/subvert host innate and adaptive immune responses

4) replicate successfully, using host resources

5) exit and transmit to a new host

4 main functions of the immune system

1) antimicrobial function: prevent/limit infection

2) tumor/tissue homeostasis: identify + eliminate damaged cells

3) regulation: prevent inadvertent damage to the host

4) immune memory: prepare for future exposure to previous pathogens

how does our immune system know what is “self?'“

we label our cells with Major Histocompatibility Complex 1 (MHC 1) proteins

MHC 1 proteins

helps our immune system recognize whether cells are “self”

every nucleated cell in our body expresses MHC 1 except red blood cells (why we can donate RBCs and receive blood transplants)

3 lines of defense against pathogens

1) barriers (keeps pathogens out)

physical barriers

mechanical barriers

chemical factors

normal microbiome

2) innate immune response (hours to days)

phagocytes (innate immune cells)

complement proteins

inflammation/fever

3) adaptive immune response (weeks to years)

B cells, T cells, antibodies

physical barriers

blocks pathogens from entering the body

ex: skin, epiglottis, eyelids, tight junctions b/w epithelial cells

mechanical barriers

mechanical actions that remove microbes + debris

ex: shedding of skin cells, cilia movement in respiratory tract, sneezing, coughing, tears

chemical factors

proteins + other compounds produced by the body that inhibit or kill microbes

ex: gastric juices, sebum, antimicrobial peptides produced by barrier tissues

normal microbiome

microorganisms (fungi, bacteria, viruses) that aren’t pathogenic + are found all over the human body

how does the normal microbiome compete with pathogens?

1) compete for nutrients

2) produce toxic substances

3) stimulate host immune system

4) take up space (compete for attachment)

2 main tissue systems with critical barrier function

1) skin

2) mucous membranes (gastrointestinal, urogenital, respiratory tracts and ocular system)

how important is the skin as a barrier to infection

the skin is the body’s primary + most vital physical line of defense against infection

30-50% mortality rates due to infection in severe burn patients

mucous membranes

lubricate many organs and body cavities to protect against pathogens

where most infections start; most pathogens get in via the mucous membranes

3 main components of the immune response

1) proteins

2) cells

3) anatomy (tissues/organs)

primary vs. secondary lymphoid tissues

primary: sites were immune cells are produced (thymus and bone marrow)

secondary: sites were the adaptive immune cells are located with antigens (spleen and lymph nodes)

bone marrow

bone tissue containing progenitor stem cells - produce all immune cell types, red blood cells, and platelets

thymus

site of T cell maturation (T cells are an essential cell type of the adaptive immune system)

lymphatic system

consists of specialized vessels that drain fluid (lymph) from tissues

lymph nodes

interspersed along the vessels of the lymphatic system

function to concentrate antigen and immune cells

also critical for initiating adaptive immune responses against most pathogens that enter through the skin or mucus membranes

spleen

organ that initiates adaptive immune system responses against pathogens that enter through the blood

bone marrow

site of hematopoiesis that generates myeloid cells and lymphoid cells from common progenitor cells

myeloid cells are innate; lymphoid cells are adaptive

phagocytes

function to surround, engulf (“eat”), and break down microbes, small particles, and apoptotic host cells

key phagocytes

1) neutrophils

2) macrophages

3) dendritic cells

granulocytes

innate cells that possess cytoplasmic granules pre-filled with inflammatory and mediators

neutrophils, basophils, eosinophils, and mast cells

neutrophils

type of granulocyte that is always first on the scene of infection to ingest bacteria + cellular debris through phagocytosis

key source of pus

netosis

process where neutrophils release their DNA to form sticky “nets” to trap bacteria

eosinophils

type of granulocyte that is high in parasitic worm (helminth) infections and allergies

mast cells

type of granulocyte that rapidly secrete proinflammatory factors (Histamine) in response to infections

activated when IgE receptor binds antigen → releases histamine → causes inflammation + calling in other immune cells

antigen

substance (from a microbe or self) that stimulates an immune response

antigen presentation

process where antigens are captured by APC (antigen presenting cells) and processed into peptides that are loaded into MHC and “presented” on the surface of APC to activate T cells

3 types of antigen presenting cells

1) dendritic cells - most “expert” at antigen presentation

2) macrophages - pretty good at antigen presentation

3) B cells

lymphocytes (T and B cells)

white blood cells that form the core of the body’s adaptive immune system

each B and T cell has a unique/variable surface receptor that responds to a specific antigen

antibodies

type of protein that are the secreted version of B cell antigen receptors

don’t directly kill; they tag foreign antigens for removal by other immune cells or protein factors

3 main ways antibodies contribute to immunity

1) neutralization - antibodies bind directly to pathogens to block them from entering healthy host cells

2) opsonization - antibodies coat surface of pathogen, flagging them so phagocytes can engulf them

3) complement activation - antibodies trigger the complement system to clear the infection

the complement system

consists of over 30-50 plasma and cell-surface proteins that work in an enzymatic cascade to opsonize, inflame, and lyse pathogens

what’s the role and function of major protein components in the complement system?

C3 - the most abundant and central protein of the entire complement system; splits into:

1) C3a - recruit immune cells (rapid response + amplification of immunity)

2) C3b - deposit on the surface of pathogens + opsonizes (tags) them to be eaten

C5 - activated by C3

1) C5a - recruit immune cells (rapid response + amplification of immunity)

2) C5b - anchor that initiates the assembly of the MAC (Membrane Attack Complex) on the pathogen

• doesn’t kill gram-positives or bacteria w/ capsules

3 ways the complement system controls infection

1) amplifies inflammation

2) increases phagocytosis

3) directly kills pathogens

cytokines vs. chemokines

small proteins that act locally and at a distance

cytokines: responsible for cell-to-cell communication during an immune response

chemokines: direct traffic; draw immune cells towards sites of infection/inflammation