The Fish Immune System

What does the immune system do?

War

Fish vs. Everything

Enemy PathogensEnemy Pathogens

Front LinesFront Lines

HomeHome

Self

The good bits that are

supposed to be there

The bad stuff: bacteria,

fungi, viruses, cancer

Foreign

Inside the LiverInside the Liver

““Gee Adjwoa, I Gee Adjwoa, I really like the really like the

bling on your cell bling on your cell phone”phone”

ComplementComplementA defensive protein A defensive protein

made by the liver and made by the liver and secreted into the secreted into the

blood. Primary target: blood. Primary target: Gram negative Gram negative

bacteria.bacteria.

Membrane bi-layer

Peptidoglycan layer

Gram Neg Gram Pos

Complement molecules begin to assemble a complex on the membrane of Gram (-) bacteria

Complement forms a channel through the cell wall

ComplementComplement

Recognizes Gram Recognizes Gram (-) bacteria(-) bacteria

Lysozyme

Lysozyme• Dissolves Gram (+)

bacterial cell walls• Found in

– Blood– Mucus– Eggs

L

Mines•Blood Proteins•Always there and ready•Work in complexes•Identify foreigners•Destroy or disable

Lymphocyte

Antibodies

AntibodiesAntibodies: Blood : Blood proteins that bind proteins that bind to foreigners. Made to foreigners. Made by lymphocytesby lymphocytes

Antibody Molecule

Variable BindingRegion

Antibody Anatomy

Antibodies bind all over a Rhabdovirus and block it from

infecting a cell.

Antibodies recognize foreign antigens on an “ich” parasite and mark it for

destruction.

Location of the Thymus in a Grass Carp

Self Antigen

“Lymphocyte Must Die”

Thymocyte

Life and Death in the Thymus

Plasma cell

B-Cell

AntigenMoreIdenticalB-Cells

Memory Cell

Memory cells: The Lymphocyte Barracks

T-Lymphocyte

Virus-infected cell

ViralProteins(antigens)

Cell Killing Chemicals fromthe T-cell

T-Cell

AntigenMoreIdenticalT-Cells

Memory Cell

Memory cells: The Lymphocyte Barracks

B-cells: Secrete antibodies that bind to

antigens on foreign things

T-cells: Attach to and kill infected cells with foreign

antigens

Lymphology• Self reacting lymphocytes weeded

out by thymus• Lymphocytes proven useful

proliferate to make more highly trained fighter pilots (B&T), and…

• Copies of useful lymphocytes are put in the barracks in case the same enemy attacks again.

Macrophages “Big Eaters"

Macrophage

USS Macrophage

Macrophages asBig Eaters

MacrophageDiets

Bacterial Cell Walls

Cell with Compliment

Cells with Antibody Flags

Vacuoles containing bleach (brown) and peroxide (green) fuse with a vacuole containing a live bacterium

More Tricks: Macrophages Searching out

Foreigners

Normal cells with MHC “locks” Parasite with fake lock

A roving macrophage detects a parasite trying to hide among a layer of fish cells.

Macrophages Even Run a School for

Lymphocytes

Macrophage Macrophage eating a bacterium

Macrophage digesting a bacterium

Macrophage using bacterial bits to educate lymphocytes.

1 2

3 4

Macrophage Functions

•Eat and kill bad cells•Check cell codes (MHC)•Run a lymphocyte school

Eosinophils

Eosinophils

The eosinophil dumps parasite-killing chemicals on a parasitic worm somewhere inside of a fish.

The worm has been “flagged” by antibody molecules

Eosinophils

Neutrophils

Neutrophils

Neutrophils

•Dump toxins on flagged cells

(chemical weapons!)

NeutrophilsNeutrophils

Mediate immune Mediate immune responsesresponses

Other Tanks and Planes

•Neutrophils: Chemical warfare, generals

•Eosinophils: Chemical warfare on parasites

Natural Killer Cells (NK)

Foreign cellsVirus infected cellsProtozoa

Armed CheckpointsArmed Checkpoints

The Spleen

The Spleen