In many studies, investigators report not the date of appearance of a variant but the date of appearance of the specific antibody to it.
However, it is unclear which organelles are positive to the antibody.
At interview, a blood sample was collected and assayed for influenza antibodies.
This time is determined as the cycle at which the number of parasites exceeds the antibody trigger level plus a specified lag time.
Also, the persistence of serum antibodies makes it difficult to differentiate between previous and recent exposures to a pathogen.
Furthermore, for immunological analysis it is difficult to exclude the possibility that the parasites carry antibody derived from the host.
Potentially harmful antibodies directed at fetal antigens are thereby 'mopped up'.
We have also reviewed studies involving animal models, the analysis of human antibody sequences and studies of, and using, computer modelling and crystal structure.
