Columbia College mini-lecture

Philippe Henry PhD, Thursday April 9th 2015

A broad overview of the immune system

Based on chapters 1 & 2 of Kuby, Immunology (6th edition) 2007

Outline:- background on importance of the immune system

- innate and adaptive response

- cells of the immune system (time permitting)

The principal function of the immune system is to protect the host against pathogenic microbes.

Overview of the immune system

Immune system

Innate (nonspecific)

1st line of defense

Cellular components

Humoral components

Adaptive (specific)2nd line of defense

Cellular components

Humoral components

Innate immunity is present in all multicellular plants and animals but only vertebrates have adaptive immunity.

Innate Immunity is ubiquitous

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Innate Immunity: cellular and molecular mechanisms predeployed before an infection and poised to prevent or eliminate the invader

- skin, mucous membranes, stomach acidity, phagocytes

- 1st line of defense

Adaptive Immunity: develops in response to infection and adapts to recognize, eliminate and remember the invading pathogen

- contingent on the innate response: signal

- antigen presenting cells, lymphocytes, antibodies

- 2nd line of defense

Innate Immune Response

• Recognition– Self/Non-self

Discrimination

• Response– Effector: neutralizes/

eliminates invader– Memory: prevents

second infection; “educates” the immune system for later attacks

Adaptive Immune Response

• Primary lymphoid organs: thymus and bone marrow is where lymphocytes mature

• Secondary lymphoid organs: lymph nodes, spleen, mucosa-associated lymphoid tissues and gut-associated lymphoid tissues provide sites for mature lymphocytes (antigenically committed) to interact with antigen

• Connected via lymphatic vessels and blood

Cells of the immune system

Immune system

Myeloid cells

Granulocytic

NeutrophilsBasophils

Monocytic

MacrophagesKupffer cells

Dendritic cells

Lymphoid cells

T cells

Helper cellsSuppressor cellsCytotoxic cells

B cells

Plasma cells

NK cells

-lymphocytes ( T and B) and antigen-presenting cells

-connect innate and adaptive responses

Key Cells & Overview of their Function

Major Phagocyte

Minor Phagocyte

Cells of the immune system: innate• Phagocytes

– Monocytes/macrophages– Dendritic cells

• Basophils and mast cells• Platelets• NK cells

Phagocytes – 1) macrophages• Ingest and digest

whole microbes and present Ag to helper T cells

• CD14

Phagocytes – 2) neutrophils

- first to arrive at site of injury playing a key role in the front-line defense against invading pathogens

- express & release cytokines: amplify inflammatory reactions by other cells

- release soluble anti-microbials

• Are complicated• Excellent phagocytes• Antigen-presenting cells

Phagocytes – 3) dendritic cells

Basophils and Mast cells

• Allergies• Mast cells are anti-

parasites• Mast cells are minor

phagocytes

Natural killer (NK) cells

• large granular lymphocytes

• Kill virus-infected or transformed cells (no Ag recognition receptors)

• Cytotoxicity mechanisms not well understood

Cells of the immune system: APC

• Cells that link the innate and adaptive arms– Antigen presenting cells (APCs)

• Heterogenous population with role in innate immunity and activation of Th cells

– Examples• Phagocytes like macrophages and dendritic cells• B cells

Cells of the immune system: adaptive

• Lymphocytes– B cells

• Plasma cells (Ab producing)– T cells

• Cytotoxic (CTL)• Helper (Th)

– Th1– Th2– Th17– T-reg

- B lymphocytes mature in bone marrow

- antigen binding receptor is a membrane bound Ab

- antigen presenting cell

- binding causes cell division and differentiation into memory B cells which produce secreted Ab

- T lymphocytes arise in bone marrow but migrate to the thymus gland to mature

- T-cell receptor (TCR): Th (CD4), Tc (CD8), T reg (CD4 + FoxP3)

- T cells don’t bind antigen directly like B cells but rather ONLY when the Ag is presented with MHC on APC

Thank you