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| Maternal Passive Immunity ： ウィキペディア英語版 |
Passive immunity
Passive immunity is the transfer of active humoral immunity in the form of ready-made antibodies, from one individual to another. Passive immunity can occur naturally, when maternal antibodies are transferred to the fetus through the placenta, and can also be induced artificially, when high levels of human (or horse) antibodies specific for a pathogen or toxin are transferred to non-immune through blood products that contain antibodies like immune globulin. Passive immunization is used when there is a high risk of infection and insufficient time for the body to develop its own immune response, or to reduce the symptoms of ongoing or immunosuppressive diseases.〔(Microbiology and Immunology On-Line Textbook ): USC School of Medicine〕 Passive immunization can be provided when people cannot synthesize antibodies, and when they have been exposed to a disease that they do have immunity against.
==Naturally acquired passive immunity==
Maternal passive immunity is a type of naturally acquired passive immunity, and refers to antibody-mediated immunity conveyed to a fetus by its mother during pregnancy. Naturally acquired passive immunity can be provided during pregnancy, and through breast-feeding. Maternal antibodies (MatAb) are passed through the placenta to the fetus by an FcRn receptor on placental cells. This occurs around the third month of gestation or pregnancy.〔Coico, R., Sunshine, G., and Benjamin, E. (2003). "Immunology: A Short Course." Pg. 48.〕 Immunoglobulin G (IgG) is the only antibody isotype that can pass through the placenta, and is the most common antibody of the five types of antibodies found in the body. IgG antibodies protects against bacterial and viral infections in fetuses.〔 Immunization is often required shortly following birth to prevent diseases in newborns such as tuberculosis, hepatitis B, polio, and pertussis, however, maternal antibodies can inhibit the induction of protective vaccine responses throughout the first year of life. This effect is usually overcome by secondary responses to booster immunization.〔Lambert, Paul-Henri, Margaret Liu and Claire-Anne Siegrist (''Can successful vaccines teach us how to induce efficient protective immune responses?'' (Full text-html) ) Nature Medicine 11, S54 - S62 (2005).〕
Passive immunity is also provided through colostrum, and the transfer of IgA antibodies found in breast milk that are transferred to the gut of the infant, protecting against bacterial infections, until the newborn can synthesize its own antibodies.〔.〕 Maternal antibodies protect against some diseases more than others such as measles, rubella, and tetanus compared to the protection provided against polio, and pertussis. Maternal passive immunity offers immediate protection, though only lasting four to six months after birth.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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