BIO 341 EU Unit 1

Commensal

“Eat at the same table“

a microorganism that lives on or inside a host organism, such as a human, deriving nutrients and shelter from the host without causing disease or providing a direct, essential service

We are dependent on these species for out survival

• digests our food

• Provide vitamins

• Protect against disease

Taking antibiotics can kill commensal bacteria

Compete with pathogens for nutrients

Before birth = no commensal organisms

After birth = commensals acquired through vaginal tract when coming out (C-section babies and normal babies get them through skin/ physical touch)

microbiota

species that inhabit a particular niche in body

• gut microbiota, skin microbiota

community of living microorganisms—including bacteria, viruses, fungi, archaea, and protists—that live in a specific environment, such as in or on the human body

pathogens

an organism that can cause disease

Types of pathogen:

• bacteria

• Virus

• Fungi

• Internal parasites

opportunistic pathogen

Only causes disease in the host if the immune system is weakened or if organism gets in the “wrong” place

Barriers against infection

Skin = tough, impenetrable barrier of epithelium

• Can be breached by wounds and burns

• Antiseptic procedures have aided in survival

Mucosal surfaces/mucosae

• Epithelial surfaces vulnerable to microbial invasion

• Opened to upside world (mouth, nose, etc)

All epithelia secrete antimicrobial peptides

Innate immune response

keeps infections highly localized = first line of defense = something you are born with

Recognizes pathogen is present

Recruits effector mechanisms to kill pathogen

• effector cells engulf pathogens

• Complement proteins = serum proteins that mark and attack pathogens

Effector cells

engulf pathogens

Send out cytokines to trigger immune response, specifically inflammation

• heat - degrade

• Redness/swelling - influx of blood to bring WBCs

Adaptive immune response

organized around an ongoing infection and adapts to nuances of the pathogen

Uses lymphocytes = white blood cells

Produces long lasting adaptive immunity

Immunological memory

lymphocytes can persist in body as immunological memory

Memory leads to acquired or protective immunity

Much fast response next time

• primary vs secondary response

Can be lifelong immunity or shorter if virus mutates

Adaptive vs Innate immunity

Innate signals adaptive

No innate immune system leads to extremely high amounts of microorganisms during infection, while no adaptive immunity leads to increasing but less than innate amounts of organisms. (shows how important innate is)

Hematopoiesis

Makes red and white blood cells

occurs in different locations depending on stage of life

Relative abundance

• Neutrophil - 50-75% (innate immunity fighter)

• Eosinophil - 1-6%

• Basophil - <1%

• Monocyte - 2-10%

• Lymphocytes - 20-50% (adaptive immunity fighter)

Hematopoietic Cell

Small lymphocyte

• production of antibodies (b cells) or cytotoxic and helper functions (t cells)

• Adaptive immune response

Plasma cell

• fully differentiated form of B cell that secretes antibodies (matured B cells)

Dendritic cell

• activation of T cells and initiation of adaptive immune response

Mast Cell

• expulsion of parasites from body through release of granules containing histamine and other active agents

• Allergies

NK cells

• kills cells infected with certain viruses (Innate)

Neutrophil

• phagocytosis and killing of microorganisms

Monocytes

• Circulating precursor cell to macrophage

Macrophage

• phagocytosis and killing of microorganisms

• Activation of T cells and initiation of immune responses

Eosinophil

• killing of antibody-coated parasites through release of granules containing histamine contents

Megakaryocyte

• platelet formation, wound repair

Basophil

• controlling immune responses to parasites

Red blood cells

• oxygen transport

Macrophages - 2 ways to kill

binding of bacteria to phagocytic receptors on macrophages induces their engulfment and degradation (eat and degrade)

Binding of bacterial components to signaling receptors on macrophages induces synthesis of inflammatory cytokines (doesn’t eat and releases cytokines)

Diversity in the immune system

immunoglobulins (Ig)

• cell surface receptors on B-cells/ B lymphocytes

T-cells receptors (TCR)

• cell-surface receptors on T cells/ T lymphocytes

Ig’s, antibodies, and TCRs all have antigen binding sites

Antigen

• recognized structure on surface of pathogen

lg, Antibodies, and TCR structure

Ig - antigen binding site, transmembrane region (heavy and light chains)

TCR - Variable regions, contact regions, transmembrane region, antigen binding site

Antibody - variable, regions, constant regions

Variable usually changes and constant doesn’t

Antibodies

Humoral immunity = immunity due to antibodies

“Mark things and bring them to macrophages and neutrophils to the them up”

Neutralization - if there is a toxin → ingestion and destruction by phagocyte

Opsonization - marking a cell → ingestion and destruction by phagocyte

lymphocyte production

produced in lymphoid tissues/organs

Primary lymphoid tissues = where lymphocytes develop and mature

Secondary lymphoid tissues = where mature lymphocytes become stimulated to respond to pathogens

lymphocytes circulation

Lymph node structure

stuff comes in at one end of the lymph node through artery or efferent lymphatics

If a pathogen drains into the lymph node it is recognized and signals are sent out

Stuff leaves in vein

B cell and T cell areas

Why are most secondary lymphoid tissues associated with the gut

because we eat and sometimes we can eat the wrong thing and it’ll usually go to the gut

Gut-associated lymphoid tissues (GALT)

Tonsils

Adenoids

Appendix

Small intestine (peyer’s patch)

Secondary lymphoid tissues

Gut associated lymphoid tissues (GALT)

Bronchial associated lymphoid tissues (BALT)

Mucosa associated lymphoid tissues (MALT)

Extracellular vs Intracellular pathogen pros and cons

Extraecllular

• immune system can recognize it better if its outside

• Pathogen can move around easier (blood stream)

• Can kill without killing entire cell

Intracellular

• can rely on host

• Can hide from immune system and to kill pathogen cell also dies

• Harder to get in cell