Immune System: Key Concepts and Cell Types for Biology Students

What is the main function of the immune system?

To protect the body from infectious agents (bacteria, viruses, fungi, parasites) and harmful substances.

What are the three main categories of leukocytes?

Granulocytes, monocytes, and lymphocytes.

Which granulocyte is the first responder to bacterial infections?

Neutrophils.

Which granulocyte specializes in parasite destruction and allergies?

Eosinophils.

Which granulocyte releases histamine and promotes inflammation?

Basophils.

What do monocytes become when they leave the blood?

Macrophages and dendritic cells.

What are the three main types of lymphocytes?

T cells, B cells, and Natural Killer (NK) cells.

What are cytokines?

Small protein messengers that regulate immune system activity.

Which cytokine fights viruses by warning neighboring cells?

Interferons (IFNs).

Is innate immunity specific or non-specific?

Non-specific.

Does innate immunity have memory?

No.

What are the physical barriers in the first line of defense?

Skin and mucous membranes.

Which cells perform phagocytosis?

Neutrophils, macrophages, dendritic cells.

What do NK cells do?

Trigger apoptosis (programmed cell death) in abnormal cells.

What does the complement system do?

A cascade of proteins that ends in cytolysis (cell bursting).

What are the 5 cardinal signs of inflammation?

Redness, heat, swelling, pain, loss of function.

What are benefits of fever?

Increases metabolism, promotes interferon activity, slows microbial growth, speeds repair.

Is adaptive immunity specific or non-specific?

Specific.

Does adaptive immunity have memory?

Yes.

What is an antigen?

A substance recognized as foreign by the immune system.

Which cells provide humoral immunity?

B cells (antibodies).

Which cells provide cell-mediated immunity?

T cells.

What do helper T cells (CD4) do?

Release cytokines, activate B cells, and activate cytotoxic T cells.

What do cytotoxic T cells (CD8) do?

Kill infected or abnormal cells using perforin and granzymes.

What do antibodies do?

Bind antigens and promote destruction by neutralization, agglutination, opsonization, and complement activation.

Which antibody is most abundant and versatile?

IgG.

Which antibody is first produced and good at agglutination?

IgM.

Which antibody is secreted in mucus, tears, saliva, and breastmilk?

IgA.

Which antibody helps activate B cells?

IgD.

Which antibody is involved in allergies and parasite defense?

IgE.

What is the difference between primary and secondary immune response?

Primary is slow and weak (first exposure); secondary is faster and stronger due to memory cells.

What is pus made of?

Dead leukocytes, pathogens, and cellular debris.

What causes allergies?

Immune overreaction to harmless substances (allergens).

Which virus infects Helper T cells and causes AIDS?

HIV