Seroconversion

In immunology, seroconversion is the development of specific antibodies in the blood serum as a result of infection or immunization, including vaccination. During infection or immunization, antigens enter the blood, and the immune system begins to produce antibodies in response. Before seroconversion, the antigen itself may or may not be detectable, but the antibody is absent. During seroconversion, the antibody is present but not yet detectable. After seroconversion, the antibody is detectable by standard techniques and remains detectable unless the individual seroreverts, in a phenomenon called seroreversion, or loss of antibody detectability, which can occur due to weakening of the immune system or decreasing antibody concentrations over time. Seroconversion refers the production of specific antibodies against specific antigens, meaning that a single infection could cause multiple waves of seroconversion against different antigens. Similarly, a single antigen could cause multiple waves of seroconversion with different classes of antibodies. For example, most antigens prompt seroconversion for the IgM class of antibodies first, and subsequently the IgG class. Seroconversion rates are one of the methods used for determining the efficacy of a vaccine. The higher the rate of seroconversion, the more protective the vaccine for a greater proportion of the population.…

In immunology, seroconversion is the development of specific antibodies in the blood serum as a result of infection or immunization, including vaccination. During infection or immunization, antigens enter the blood, and the immune system begins to produce antibodies in response. Before seroconversion, the antigen itself may or may not be detectable, but the antibody is absent. During seroconversion, the antibody is present but not yet detectable. After seroconversion, the antibody is detectable by standard techniques and remains detectable unless the individual seroreverts, in a phenomenon called seroreversion, or loss of antibody detectability, which can occur due to weakening of the immune system or decreasing antibody concentrations over time. Seroconversion refers the production of specific antibodies against specific antigens, meaning that a single infection could cause multiple waves of seroconversion against different antigens. Similarly, a single antigen could cause multiple waves of seroconversion with different classes of antibodies. For example, most antigens prompt seroconversion for the IgM class of antibodies first, and subsequently the IgG class. Seroconversion rates are one of the methods used for determining the efficacy of a vaccine. The higher the rate of seroconversion, the more protective the vaccine for a greater proportion of the population. Seroconversion does not inherently confer immunity or resistance to infection. Only some antibodies, such as anti-spike antibodies for COVID-19, confer protection. Because seroconversion refers to detectability by standard techniques, seropositivity status depends on the sensitivity and specificity of the assay. As a result, assays, like any serum test, may give false positives or false negatives and should be confirmed if used for diagnosis or treatment. ==Background== The immune system maintains an immunological memory of infectious pathogens to facilitate early detection and to confer protective immunity against a rechallenge. This explains why many childhood diseases never recur in adulthood (and when they do, it generally indicates immunosuppression). It generally takes several days for B cells to begin producing antibodies, and it takes further time for those antibodies to develop sufficient specificity to bind strongly to their specific antigen. In the initial (primary infection) phase of the infection, the immune system responds by generating weakly binding immunoglobulin M (IgM) antibodies; although they individually bind weakly, each IgM antibody has many binding regions and can thus make for an effective initial mobilization of the immune system. Over time, immunoglobulin class switching will result in IgM-generating B-cells switching to more specific IgG-generating B-cells. Levels of IgM then gradually decline and eventually become undetectable by immunoassays, while levels of immunoglobulin G (IgG) levels rise and become detectable. After the infection resolves, levels of IgM antibodies generally fall to completely undetectable levels as the immune response self-regulates, but some plasma cells will remain as memory cells to produce levels of IgG that will frequently remain detectable for months to years after the initial infection. Upon reinfection, levels of both IgM and IgG rise, with IgM antibodies having a more rapid but smaller and less sustained peak, and IgG antibodies having a slightly slower, but far greater peak sustained over a longer period of time compared to IgM antibodies. Subsequent infections will demonstrate similar patterns, with initial IgM peaks and significantly stronger IgG peaks, with the IgG peak occurring more rapidly during subsequent infections. Thus an elevated IgM titre indicates recent primary infection or acute reinfection, while the presence of IgG suggests past infection or immunization. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, the virus causing COVID-19) sometimes does not follow the usual pattern, with IgM sometimes occurring after IgG, together with IgG, or not occurring at all. Generally, however, median IgM detection occurs 5 days after symptom onset, and IgG is detected a median 14 days after symptom onset.

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