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KOCH’S POSTULATES

In the 1880s German doctor, Robert Koch, developed a series of methods for identifying which organism was the cause of a particular disease. These postulates are still in use today.This led the way for specific treatment for many disease- causing pathogens.

Response of Immune System to Disease-Causing Organisms

A. RECOGNITION: white blood cell surrounds pathogen and signals killer T cells (not shown); more T cells are produced; helper T cells signal B cellsB. MOBILIZATION: B cells produce antibodiesC. DISPOSAL: antibodies destroy pathogensD. IMMUNITY: some antibodies remain for future use (memory B cells)

Antigen-Antibody Complex

• Antibodies all have the same basic Y structure• Antibodies have different antigen binding sites designed to fit the shape of specific antigens• Antibodies bind to antigens like a lock and key to form the Antigen-Antibody Complex

INDIRECT ELISA (enzyme – linked immunoabsorbant assay)• Used to detect infection by testing patients’ blood serum for the presence or absence of antibodies against a particular pathogen • Presence of antibodies indicates the individual has been infected and that their body has launched an immune response against the disease-causing agent• Test for: HIV, Avian Flu, West Nile, Lyme Disease, Smallpox, SARS, Syphilis, Rocky Mountain Spotted Fever

Human ImmunodeficiencyVirus

Virus responsible for causingAcquired Immune Deficiency Syndrome orAIDS

Rates of Persons Aged 18–64 Years Living with a Diagnosis of HIV Infection, Year-End 2008—United States

Reported Cases in the United States, 2012

LYME DISEASE

Vector =deer tick

Avian Influenza (Bird Flu)

ELISA TEST RESULTS

ELISA data from three patients. Numbers are expressed as optical density at 450 nm. The cutoff value indicating a positive result is 0.500. Optical densities of 0.300 to 0.499 are indeterminate and need to be retested. Values below 0.300 are considered to be negative. In most cases, a patient will be retested if the serum gives a positive result. If the ELISA retests are positive, the patient will then be retested by western blotting analysis.

Positive Control

Negative Control Patient A Patient B Patient C

Assay Control

1.689 0.153 O.055 0.412 1.999 0.123

ELISA SIMULATION RESULTS

In this simulated ELISA, all reaction wells will turn light green when the chromogen substrate is added. A change in color from light green to purple indicates a positive result.