How a cell infected by a virus signals cytotoxic T lymphocytes to kill the cell before the virus replicates and spreads. This video is two minutes and 34 seconds in length, and available in Quick Time (11 MB) and Windows Media Player (23 MB). All Infection Disease Animations are located at: http://www.hhmi.org/biointeractive/disease/animations.html.

View the animation to see how one type of immune cell-the helper T cell-interprets a message presented at the surface of the cell membrane. The message is an antigen, a protein fragment taken from an invading microbe. A series of events unfolds that results in the production of many clones of the helper T cell. These identical T cells can serve as a brigade forming an essential communication network to activate B cells, which make antibodies that will specifically attack the activating antigen.

This 4-lecture series covers the basics of the immune system, how T cells work, how MHC proteins affect our susceptibility to autoimmune diseases, and the relationship between the immune system and infectious diseases.

A mini-documentary discussing the remarkable regenerative capabilities of the planarian, and how HHMI researcher Alejandro Snchez Alvarado uses them to study the biology of stem cells. This presentation is also featured on the DVD Potent Biology: Stem Cells, Cloning, and Regeneration, available for free from HHMI. This video is 11 minutes and 46 seconds in length, and available for download in Quicktime (114 MB) and Windows Media (156 MB) formats. All Stem Cell videos are located at: http://www.hhmi.org/biointeractive/stemcells/video.html.

When two different strains of influenza infect a single cell, their genetic material can mix freely, resulting in a new third strain of influenza.

Delivering a single virus to a cell allows the virus to infect the cell, replicate, and give rise to many progeny viruses. These viruses can then infect many neighboring cells.

Components of the immune system called antibodies are found in the liquid portion of blood and help protect the body from harm. Antibodies can also be used outside the body in a laboratory-based assay to help diagnose disease caused by malfunctions of the immune system or by infections.This virtual laboratory will demonstrate how such a test, termed an enzyme-linked immunosorbent assay (ELISA), is carried out and show some of the key experimental problems that may be encountered.