Submitted to: Journal of Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/16/2001
Publication Date: N/A
Interpretive Summary: One of the major concerns faced by pork producers is the economic loss caused by infectious disease in swine. Vaccine use has and will be an important part of the strategy for controlling and preventing swine diseases. Understanding the pig's immune response to infectious disease is critical to understanding how and why a vaccine may or may not work. This paper describes basic research investigating how the immune system develops in swine. Specifically, when and how does the immune system develop during fetal life. The building blocks or precursors to mature immunoglobulins or antibodies can be detected at about 40 days of gestation. The concentration and diversity of antibodies increases as the porcine fetus develops. This appears to be different than other mammals, namely mice and humans. Investigating the development of the immune system at the cellular and molecular level will provide scientists data that can be used to design additional studies investigating the pig's immune system. Collectively, this information can be used to construct better vaccines to help reduce economic losses for pork producers.
Technical Abstract: Analysis of immunoglobulin (Ig) levels and Ig isotype profiles in normal and virus-infected fetuses from gestation day (GD) 38-110 suggested that IgG and IgA, and IgM were most likely the result of de novo synthesis. Although transcripts for IgM could be recovered at GD 50 in all major fetal lymphoid tissues, those for IgG and IgA first became prominent at GD 60 in thymus, and transcription and spontaneous secretion became especially pronounced in the organ in older fetuses. Data on transcription, secretion, and serum isotype profiles suggest that although all fetal IgA and IgM may result from de novo synthesis, some IgG may result from low-level selective transplacental transport. The complementarity-determining region 3 spectratypes of thymic IgA and IgG transcripts at GD 70 and 90, respectively, were as polyclonal as that of IgM, indicating a broad repertoire of switched B cells although the VDJs expressed with switched isotypes in normal fetuses were not diversified in comparison to those from pigs exposed to environmental Ags such as age-matched virus-infected fetuses, colonized isolator piglets, and conventional adults. Thus, switch recombination in fetal life does not appear to be driven by environmental Ag and is only weakly coupled to VDJ diversification. These findings, and the fact that the oligoclonal IgA and IgM repertoires in a noninductive site of the mucosal immune system (parotid gland) become polyclonal in piglets reared germfree, suggest that initial expansion of the switched cells in the B cell compartment of fetal and neonatal piglets is not driven by environmental antigen.