Question: In the forensic science laboratory, a small, crusty yellow stain is observed on the fitted double bed sheet.

The results of the tests conducted on this stain are as follows:

Tetramethylbenzidine (TMB) test: Blue-green color within one to two seconds
Kastle-Meyer (KM) test: Pink color within one to two seconds
Alkaline phosphatase (AP) test: Positive
Prostate specific antigen (PSA) test: The protocols for the laboratory do not call for the microscopical identification of sperm.

In the capacity of a forensic biologist, include in your report your opinion regarding this stain. Explain the following in your report:

Nature of the stain: Does it contain blood, semen, or any other fluid?

Question: Describe how the clonal expansion theory explains the more rapid production of antigen specific antibodies, Helper T-cells and Cytotoxic T-cells, during a secondary infection.