The patient has a negative Dick test and a positive Schick test, which indicates that he has neutralizing antibodies against the group A streptococcus that causes scarlet fever. In both tests, the antigen that is injected is the toxin. If neutralizing antibodies are present, they neutralize the toxin and skin reactions do not occur. This indicates that the patient is immune to the specific strain of bacteria producing the disease. For example, the patient&;s negative Dick test means that he has neutralizing antibodies that will protect him against the strain of streptococcus that produces scarlet fever, but not against strains that may be associated with pharyngitis or other infections. Absence of the antibodies allows the toxin to host an inflammatory reaction, which indicates a lack of immunity. If the patient had a full complement of diphtheria-peussis-tetanus (OPT) immunizations, neutralizing antibodies against diphtheria should be present. The presence of a reaction for the Schick test is a not a test of cellular immunity, because it is an antigen-antibody reaction.