32: Host vs Parasites

Why does the immune response to parasites have to be so diverse

Parasites are very diverse (single cell v large) and have lots of life stages

Key players in an immune response to parasites

• Macrophages

• Complement

• T_H cells

• Humoral response

T_H response to helminths

T_H2

T_H2 response is pretty damaging. What mechanisms does the immune system use for ova and larvae

• IL-10

• Walling off ova

What part of a helminth infection is recognized most strongly

Anything they secrete

Response to T_H2 activation

• LOTS of cytokines

• IgE

• Activates eosinophils and mast cells

• Increased smooth muscle motility

• Increased mucus secretion

• Increased epithelial permeability

Receptor on mast cells and eosinophils that recognizes IgE

Fcε receptor

What causes degranulation of mast cells and eosinophils

Cross linking of bound IgE

Type of degranulation that eosinophils undergo

Piecemeal degranulation: more controlled and gradual

Action of T_H2 cytokines on the bone marrow

Increases eosinophil production → systemic eosinophilia

What do eosinophils follow

Mast cells

Key components in mast cell granules

• Histamines

• Eosinophil chemoattractants

What other cell shows up after mast cells and eosinophils start throwing their party

Basophils

Mechanisms helminths use to evade the immune system

• Ag masking

• Antigenic variation

• Blocks immune system components

• Evolutionary tolerance

Common clinical sign of a parasite infection in younger animals

Parasite gastroenteritis

Grades of immunity once an animal is no longer young

Resilient or resistant

Resilient

Animals do ok, but they are subclinical and high egg shedders

Resistant

Animals do great, and they are shed very few eggs

What other T_H cell helps mediate the humoral response with T_H2

T_H1

What may inform whether an animal is resilient or resistant to a parasite infection

How much T_H2 to T_H1 response it has

What types of parasites would be better fought by T_H1

Intracellular

Major cytokine released from T_H1

IFN-γ

What does IFN-γ activate

• M1

• NK cells

• CD8

Cytokine that causes T_H2 cell differentiation

IL-4

Cytokine released by T_H2 that downregulates the T_H2 response and helps with tissue remodeling

IL-10 (also for handling ova and larvae!)

What Ab can help with activating NK cells

IgG

Four functions of Abs

• Opsonize

• Agglutinate

• Immobilize/neutralize

• Lysis

Mechanisms protozoa use to evade the immune system

• Hides intracellularly

• Immunosuppression

• Ag masking: steals host proteins

• Antigenic variation: keeps host Abs outdated

How do arthropods/ticks trigger the immune system

Immune modulators in saliva

When do normal arthropods in the skin cause issues

When the host is immunosuppressed → demodectic mange

Flea bite allergy results in what type of hypersensitivity reaction

1 → 4 → granuloma

What parasite do we have a vaccine for

Leishmani