Infection and Immunity Wk 8 - Lesson 55

What is phagocytosis?

internalization of particulate matter by cells by a process of engulfment, in which the cell membrane surrounds the material eventually forming and intracellular vesicle (phagosome) containing the ingested material

What are types of phagocytic cells?

macrophages and neutrophils

What do phagocytic cells do?

trap and kill pathogens, trap and degrade cellular derbis

What is chemotaxis?

cellular movement in response to chemical signals in the environment

What is an example of chemotaxis?

release of chemokines to attract phagocytes to the infected area or damaged tissue

What is the phagosome?

intracellular vesicle formed when particulate material is ingested by a phagocyte

What is a phagolysosome?

intracellular vesicle formed by the fusion of phagosome and a lysosome and in which the ingested material is broken down

What are pattern recognition receptors?

PRRs; receptors of the innate immune system that recognize common molecular patterns on pathogen surfaces

What are toll-like receptors?

TLRs; most important group of PRRs for the innate immune response

What are skin defense mechanisms?

skin barrier, sebum production, desquamation

What are respiratory tract defense mechanisms?

respiratory mucociliary flow, coughing, and sneezing

What are GI tract defense mechanisms?

stomach acid, peristalsis, mucus production

What is skin-associated lymphoid tissues?

SALT; not a direct physical/chemical/mechanical defense mechanisms; consist of cells of the innate and adaptive immune system; serve as sites for immune cell activation and proliferation

What are the SALT cells of the innate immune system?

keratinocytes and langerhans cells (LCs)

What are keratinocytes?

specialized epithelial cells that can act as APCs and secrete cytokines that induce inflammatory reactions

What are Langerhans cells?

type of dendritic cell that can phagocytose, migrate from the epidermis to regional lymph nodes where they differentiate and function as potent activators of skin-trophic naive T cells

What are the four phases of phagocytosis?

chemotaxis, adherence, ingestion, destruction

How do phagocytic cells recognize microbes?

PRRs recognize PAMPs on the microbes and by recognizing opsonins

What does the interaction between TLRs and PAMPs allow for?

-microbial recognition, attachment, followed by phagocytosis

-signals activate genes in the phagocytic cell that result in production of cytokines

What is the common progenitor cell of neutrophils and macrophages?

myeloid progenitor cell

What does macrophages have in common with dendritic cells?

they are both sentinel cells and antigen-presenting cells

What are macrophages capable of in terms of phagocytosis?

sustained killing of microbes

What do macrophages secrete?

chemotactic cytokines to call in neutrophils

What type of healing are macrophages involved in?

wound

Where do neutrophils reside?

bone marrow, blood

Which is the first cell to respond to infections?

neutrophils

What is a neutrophils lifespan like?

short; 6-10 hours; phagocytosis leads to death of cell; rapidly exhausted

What do dying neutrophils attract?

macrophages

What type of neutrophils do not undergo proliferation?

mature, circulating neutrophils

How come neutrophils are very fast and first to respond?

active immediately after release from bone marrow

What are neutrophils incapable of?

sustained killing

What cell is typically the first responder to a bacterial infection?

neutrophils

Where do natural killer cells originate from?

lymphoid progenitor cell

What are NK cells lacking?

receptors

Where do NK cells migrate to?

bone marrow to blood to tissues

What do NK cells do?

kill (virus) infected host cells and host tumor cells; do not kill microbes directly but the host cells that they infect

How do NK cells recognize target cells?

-antibody attached to host cells (ADCC)

-complement proteins attached to host cells

-stress molecules being expressed by host cells

-abnormal cells that do not express MHC-1 molecules

How do innate immune system cells communicate?

direct contact cell-to-cell and indirect via signaling molecules

What are cytokines?

small soluble proteins secreted mainly by cells of the immune system to participate in cell-to-cell communication

What is the function of cytokines?

signals for cell survival, proliferation, differentiation, function; regulates immune responses

How do NK cells kill host cells?

by poking holes