Introduction to Host Response

Learning objectives

Describe the function of the immune system

Compare & Contrast innate immunity and adaptive immunity

Describe the role of B-cells and T-cells in the immune system

List the five classes of antibodies (immunoglobins) and describe the functions of each antibody class

Describe the complement system and explain the role it plays in the immune response

Define the term host response and describe its primary function

Purpose of the immune system

Protect and defend the life of the individual (the host), by identifying foreign substances in the body and developing a defense against them

The way an individual’s body responds to an infection is known as host response.

Two parts of the immune system

innate

adaptive

Innate immunity

Present at birth

Always present

Does not improve with repeated exposure to an infectious agent

Cells include: Neutrophils, Monocytes, Macrophages, Eosinophils, Basophils, Mast Cells, NKT-lymphocytes

Adaptive/acquired immunity

Develops throughout life after exposure to antigen

Acquired= process of repeated exposure

Memory develops, which may provide lifelong immunity to reinfection to the same infectious agent

Cells include: T-lymphocytes, B-lymphocytes

Components of the immune system

cellular defenders

complement system

Lymphocytes

play an important role in recognizing and neutralizing foreign invaders

belong to adaptive immunity

3 types: B, T, NK-lymphocytes

B-lymphocytes

originate from bone marrow

B-cells

• Plasma B-Cells (produce antibodies)

• Memory B-Cells (remember exposed pathogens)

Plasma B cells (produce antibodies/remember exposed antigens)

produce antibodies

Memory B cells (produce antibodies/remember exposed pathogens)

remember exposed pathogens

Antibodies

Collaborate with other leukocytes and complement system to eliminate the offending agent

Also known as immunoglobins: IgM, IgG, IgA, IgE, IgD

IgM

• Found on B cells (circulates in bloodstream)

• Largest therefore, cannot exit the circulatory system easily

• Earliest to appear at a site of infection

• Indicates a recent infection

IgG

• 4 types

• Most abundant of all immunoglobulins

• Found in blood and tissue

• Effective against bacteria, viruses, and fungi

• Only one that can pass through the placenta

IgA

• 2 types serum and secretory

• Found in tears and saliva

• Most important for us

• Prevents bacteria and viruses from adhering to mucous membranes

Which immunoglobulin most pertains to us as dental hygienists?

IgA

IgD

Secreted in the smallest concentrations

• Function is a mystery

IgE

• Only found in mammals

• Major defense against parasites

• May defend against cancer

• Responsible for most allergic reactions and anaphylaxis

T-lymphocytes

mature in thymus

T helper cell (CD4)

regulates differentiation and maturation of B cells and activation of cytotoxic T cells + macrophages

doesn’t directly neutralize or clear pathogens

T cytotoxic cell (CD8)

directly attacks viral infected cells or tumor cells by releasing perforin (punches holes through plasma membrane of target cell)

indirectly attacks by producing antiviral and antitumor cytokines such a TNF-a and IFN-y

Tm lymphocyte

memory

remembers past exposure so immune response is faster and stronger

NKT-lymphocytes (NKT)

cytokine secretion

very first lines of defense against some types of bacterial and viral infections

Complement system

Offers an added layer of defense that is needed against pathogens

Ability to evade and outwit the cellular defenders

Made up of proteins

Lyse bacteria

4 functions: opsonization, membrane attack complex, phagocytosis, clearance