Answer
An antibody titer is a measure of how much antibodies are in the blood. When a subject is infected by a pathogen for the the first time, the host's immune system mounts an immune response and secretes antibodies to destroy or neutralize the antigens of the pathogenic microbe. This is called a primary response-- most of the antibodies produced by the plasma cells are of the IgM class Also, if a subject is exposed to an antigen for the first time, but this time by injection of killed or weakened microbes -- a process called vaccination--the immune system of the subject will respond in a manner similar to the first response. In both cases the reactions are called primary, because the immune cells are seeing the antigen for the first time. In the first case, however the immunity acquired is called naturally acquired immunity because the subject came into contact in the natural/normal-- way by being exposed to something or someone who/or that was carrying the pathogenic organism . By contrast in the second case the pathogen was modified by man and introduced deliberately and artificially into the subject. For these reasons the immunity gained/acquired is appropriately designated artificially acquired immunity.
If Tariq had been exposed to the mumps virus before -- either naturally or by vaccination--his memory cell would mount a rapid and vigorous secondary response and his serum would very quickly have a high titer of anti-mums virus IgG antibodies, after his exposure to his mumps infected sister. However if he had not been exposed to the mumps virus before being infected by his sister, his immune system would mount a primary response and his serum would develop high levels of antibodies ( mainly IgM) produced by plasma cells.
Work Step by Step
Immune reactions do not produce single classes of antibodies in response to a challenge. However, at different stages, one class will predominate.
