Antibody response to chlamydia agents: lack of immunoglobulin M antibodies during the secondary immune response.

Intramuscular inoculation of the monkey with a massive dose of Chlamydia agent particles resulted in the production of high levels of immunoglobulin M antibodies. These antibodies were broadly specific and reacted to high titers with heterologous antigens. Challenge inoculation of the same monkeys with heterologous Chlamydia agent particles resulted in the production of increased levels of immunoglobulin G but not immunoglobulin M antibodies. Some immunological implications of these results are discussed.