6. Immunity Against Pathogens

What are the main types of pathogens?

Bacteria, viruses, parasites, and fungi

What are the general characteristics of bacteria?

Microscopic, single-celled, prokaryotic organisms; can be extracellular or intracellular

What are the general characteristics of viruses?

Acellular particles with a protein coat surrounding genomic material; must enter host cells to propagate

What are the general characteristics of parasites?

Take advantage of a host for habitat and nutrition; can be single-celled protozoans, multicellular helminth worms, or arthropod ectoparasites

What are the general characteristics of fungi?

Can exist outside a host but invade and colonize when given the opportunity; can be single-celled or multicellular

What are the main routes of transmission for infectious agents?

Direct contact, inhalation, ingestion, injection, mating, and through wounds

How do extracellular bacteria cause disease?

By inducing inflammation, tissue injury, and producing toxins (endotoxins and exotoxins)

How do viruses cause cellular damage?

By disrupting cell function through viral replication, leading to cell death (lytic infection)

What are the main mechanisms of innate immunity against extracellular bacteria?

Phagocytosis, complement activation, and inflammatory response

What is the primary adaptive immune response against extracellular bacteria?

Humoral immunity (antibody production)

How do intracellular bacteria evade the immune system?

By replicating within host cells, making them inaccessible to antibodies

What is the main adaptive immune response against viruses?

Cytotoxic T lymphocytes (CTLs) that kill infected cells, and antibodies that block virus binding and entry

What is a common strategy used by viruses to evade the immune system?

Antigenic variation, leading to antigenic drift and shift (e.g., in influenza viruses)

How do some bacteria evade phagocytosis?

By having polysaccharide-rich capsules

What is a method used by some bacteria to inhibit complement activation?

Having capsules with sialic acid residues

What are the main barriers in the immune system's defense against pathogens?

Skin, mucous membranes, and secretions (e.g., tears, saliva)

How does the skin act as a barrier to pathogens?

Provides a physical barrier and secretes antimicrobial substances

What is the role of mucous membranes in immunity?

Trap pathogens and contain antimicrobial substances

What are the key components of innate immunity?

Physical barriers, phagocytes, natural killer cells, and complement proteins

What is the function of phagocytes in the immune response?

Engulf and destroy pathogens through phagocytosis

What are the two main types of adaptive immune responses?

Humoral immunity (antibody-mediated) and cell-mediated immunity

What is the role of B lymphocytes in the immune response?

Produce antibodies that neutralize pathogens and mark them for destruction

How do cytotoxic T lymphocytes (CTLs) respond to infected cells?

Kill infected cells by inducing apoptosis (programmed cell death)

What is a common mechanism by which fungi cause disease?

Enzymatic degradation of host tissues and evasion of immune responses

How do some parasites evade the immune system?

By altering their surface antigens or hiding within host cells