Topic 6: Immunity & Antibodies

How do Pathogens Enter the Body

• inhalation — coughing, talking, sneezing

• ingestion — eating food contaminated with pathogens

• direct contact — touching skin to skin or through bodily fluids

• vector — an organism that carries infections (like mosquitoes)

• fomites — inanimate objects like dust that might land on the skin, eyes, mouth etc

what are Barriers that Protect the Body

• skin — physical barrier

• stomach acid — kills bacteria due to it’s low pH

• gut & skin flora — natural bacterial flora competes with pathogens for food and space

• mucus — traps pathogens in the respiratory track

• lysozyme — secretion of mucosal surfaces (tears, saliva, mucus) these damage bacterial cell walls so they burst

• sebum — oily substance produced by the skin that contains chemicals that inhibit the growth of microorganisms

what are some Non-specific Responses

• inflammation

• fever

• lysozyme action

• interferon

• phagocytosis

describe inflammation

damaged tissues trigger the release of chemicals like histamines (released by basophils). Causing the vasodilation of blood vessels which leads to heat and redness. Increased temperature reduces reproduction rate of pathogens. Histamines make capillary cells more permeable, plasmas leaks out containing leucocytes and antibodies. this causes swelling and pain. Antibodies disable the pathogen and they are destroyed by phagocytosis.

describe a fever

reduces the reproduction of pathogen

describe lysozyme action

it’s an enzyme found in secretions like tears and mucus that kills bacterial cells by damaging their cell wall

describe interferon

they’re proteins that inhibit the reproduction of viruses within the cell. An interferon diffuses from the cell where it has been made into the surrounding cells. It binds to receptors of uninfected cells which stimulates a pathway that makes the cells resistant to infection

describe phagocytosis

phagocyte detect the presence of the pathogen when receptors on its cell surface bind to antigens on the pathogens. Then engulfs the pathogen. the pathogen is isolated in the phagosome, lysosomes release lysozymes in to digest the pathogen, destroying it

how do antibodies work by agglutination

clumping pathogens together

how do antibodies work by neutralizing toxins (neutralization)

blocking toxins or cell entry

how do antibodies work by blocking access to human cells

When antibodies bind to antigens, it prevents the antigen from fitting in the receptor which means it can’t get inside the cell.

how do antibodies work by opsonization

marking for phagocytosis

how do bacterial antibiotics work?

kill bacteria by destroying their cell wall thus causing them to burst

how do bacteriostatic antibiotics work?

inhibit the growth of bacteria by stopping protein synthesis and production of nucleic acids so the bacteria can’t grow and divide

why do antibiotics have no effect on eukaryotic cell and viruses?

eukaryotic cells do not have a cell wall and their ribosomes are a different size (which means that antibiotics cannot bind to them). and viruses do not possess either a cell wall or ribosomes.

describe stage 1 humoral response of the immune system

A macrophage engulfs and digests the pathogen via phagocytosis. It displays the antigen on its surface using MHC proteins becoming an APC. T helper cells with complementary receptors bind to the antigen on the APC, triggering clonal expansion of T helper cells by mitosis. Activated T helper cells release cytokines that stimulate B cells to divide into B memory and B effector cells. B effector cells differentiate into plasma cells that secrete antibodies.

describe stage 2 cell mediated response of the immune system

A macrophage engulfs and digests the pathogen via phagocytosis. It displays the antigen on its surface using MHC proteins becoming an APC. T helper cells with complementary receptors bind to the antigen on the APC, triggering clonal expansion of T helper cells by mitosis. Activated T helper cells secrete cytokines. T killer cells recognize antigen of infected cells. Cytokines activate clonal expansion of T killer cells. They release perforins and granzymes so the infected cell undergoes lysis. T memory cells form in-case of re-infection.