Week 2 - Host Defenses Against Bacteria and Fungi

3 types of fungi

Fungi (mold), yeast, and dimorphic fungi

Main difference between types of fungi

Mold: grows the same at environment and body temps (big circles of different colors/textures)

Yeast: bacteria-like growth at both environment and body temps

Dimorphic: mold-like growth at environment temps and bacteria-like growth at body temps

Molds

• Multicellular and multinuclear

• Grow in long, thin filaments called hyphae

• Growth occurs at end of hyphal tip

Yeasts

• Unicellular

• Oval shaped and much larger than most bacteria

• Some have capsules

• Grow by division - budding or binary fission

Dimorphic fungi

• 2 distinct morphologies that grow at different temps

• Filamentous, mold, forms at lower temps

• Yeast forms at higher temps (body temps)

Types of immunity

• Innate immunity

• Acquired immunity

Innate immune system

• First line of defense against pathogens

• Includes: the skin, mucus, stomach acid, mechanical methods of removing debris, natural flora already in/on body, macrophages & neutrophils

What are opsonins?

Immune components that bind to pathogen surface and help phagocytic cells "catch" the pathogen easier

• can be innate (CRP, MBP) or acquired (Ig, IgG)

Job of dendritic cells

• Located in mucus membranes

• Have long membrane extensions that allows quick movement throughout body

• Act as antigen presenting cells

• Can produce cytokines involved in immune response

What are NK cells?

• Natural killer cells, innate lymphocytes derived from bone marrow

• Can lyse and kill target cells (mainly target viruses & tumors)

• Do not require antigen stimulation to attack

• Can kill either with granzyme and perforin or by inducing apoptosis

Acquired immune system

• Takes at least a day to generate an immune response

• Contains memory abilities for repeat infections

• Includes: B-cells, T-cells, antibodies

B-cells

• Lymphocytes, distinctly different from T-cells

• B1 formed in liver of embryos (only really present/used in embryos)

• B2 cells develop in bone marrow

• B2 cells have cell receptors (BCR) on their surface, used to recognize free, unprocessed antigens

What are the functions of B-cells antibodies?

Can be one of many:

• Anti-transporter

• Anti-capsules, anti-LPS, anti-surface antigen

• Complement activation

• Anti-toxins

• Anti-adhesins, anti-invasions

T-cells

• Can have memory. Receptors on surface can recognize antigens that have been processed and presented by MHCs

• Develop in thymus

• 2 types: helper cells & cytotoxic cells

T helper cells (Th)

Have a cluster of differentiation (CD) 4 on their surface

Recognizes MHC II

(low recognizes high)

Cytotoxic T cells (Tc)

Have CD8 on their surface

Recognizes MHC I (high recognizes low)