On the basis of the analysis of antibodies, could the crime lab determine whether a sample of body fluid is blood plasma or semen?
I'm not a forensic biologist, but I would have to answer this way: 1) On the basis of antibodies, I don't know if they could differentiate between blood plasma and semen. 2) On other factors, such as enzymes and cell types present, I would think they could easily differentiate.
Different classes of antibodies are present or more likely to be present in different bodily compartments so i would presume that the common IgG or IgM would be more prevalent in the plasma and perhaps IgA in the semen. Apart from antibodies like forensics_guy says specific enzymes will be in each sample and things like fibrinogen which help clot the blood could be tested for and found in plasma, and if sperm cells are present in the semen there would be high incidence of mitichondria! hope that helped!