The antigen concentration is not used to deduce the infection pathway because the immune system of the body might fight off the antigen. The lymphocytes, which are a part of the immune system helps in the production of the antibodies, and destroying the antigens. Therefore, the use of the antigen concentration here may result in skewed results as the antigens might get destroyed by the immune response of the body. Moreover, the response of different individuals to different concentrations of the antigens will be different.