Description: Segment 1 Dr Ian Gilliland introduces Prof. Turk, Professor of Pathology at the Institute of Basic Medical Sciences. Prof. Turk explains what a hypersensitivity reaction is and what the two types of reaction are. He says that the prototype of all delayed hypersenstivity reactions is the tuberculin reaction. A table shows comparisons of different hypersensitivity reactions and Turk explains the data. Another table compares appearances of different reactions. A third table compares sensitisation of different reactions. Turk then explains the causes of delayed hypersensitivity, which are also listed in a table. Time start: 00:00:00:00 Time end: 00:05:29:14 Length: 00:05:29:14 Segment 2 Next, Turk gives information on other types of delayed hypersensitivity reactions, including the homograft reaction. Turk then explains the phases of delayed hypsersensitivity with the aid of a chart with movable parts. He changes the parts as he explains the phases. The stages of reaction are listed in a table. Time start: 00:05:29:14 Time end: 00:09:01:03 Length: 00:03:31:14 Segment 3 Turk next talks about lymphocytes found in the bone marrow. He explains the two types, B and T lymphocytes and how they may produce delayed hypersensitivity reactions. Next, Turk looks at histological sections of lymphocyte cells to illustrate their departmentalisation. A series of slides of lymph nodes is shown, and Turk explains the differences between them. Time start: 00:09:01:03 Time end: 00:14:25:15 Length: 00:05:24:12 Segment 4 Turk discusses a lymph node's response to an injection of an antigen. He discusses another picture of an electron micrograph of a plasma cell. Next, he talks about what happens during a relatively pure cell-mediated immune reaction. A series of slides of lymph nodes is seen as Turk explains the series of events that occur in this reaction. Time start: 00:14:25:15 Time end: 00:20:14:00 Length: 00:05:48:10 Segment 6 Turk once again uses the movable chart to explain the recognition of antigen by lymphocyte cells. End credits. Time start: 00:25:29:00 Time end: 00:27:16:15 Length: 00:01:47:15