Abstract
BackgroundThe first hours after antigen stimulation, interactions occur influencing the outcome of the immunological reaction. Immunoglobulins originate in blood and/or are locally synthesized. The transfer of Ig isotypes (Igs) in the udder has been studied previously but without the possibility to distinguish between the endothelium and the epithelium. The purpose of this study was to map the Ig transfer through each barrier, separately, and Ig transfer in the local lymph nodes of the bovine udder during the initial innate immune response.MethodsThe content of IgG1, IgG2, IgM, IgA and albumin (BSA) was examined in peripheral/afferent mammary lymph and lymph leaving the supramammary lymph nodes, and in blood and milk before (0 h) and during 4 hours after intramammary challenge with Esherichia coli endotoxin in 5 cows.ResultsIgs increased most rapidly in afferent lymph resulting in higher concentrations than in efferent lymph at postinfusion hour (PIH) 2, contrary to before challenge. Ig concentrations in milk were lower than in lymph; except for IgA at 0 h; and they increased more slowly. Afferent lymph:serum and efferent lymph:serum concentration ratios (CR) of Igs were similar to those of BSA but slightly lower. Milk:afferent lymph (M:A) CRs of each Ig, except for IgG2, showed strikingly different pattern than those of BSA. The M:A CR of IgG1, IgM and IgA were higher than that of BSA before challenge and the CR of IgA and IgG1 remained higher also thereafter. At PIH 2 there was a drop in Ig CRs, except for IgG2, in contrast to the BSA CR which gradually increased. The M:A CR of IgM and Ig A decreased from 0 h to PIH 4, in spite of increasing permeability.ConclusionThe transfer of Igs through the endothelium appeared to be merely a result of diffusion although their large molecular size may hamper the diffusion. The transfer through the epithelium and the Ig concentrations in milk seemed more influenced by selective mechanisms and local sources, respectively. Our observations indicate a selective mechanism in the transfer of IgG1 through the epithelium also in lactating glands, not previously shown; a local synthesis of IgA and possibly of IgM, released primarily into milk, not into tissue fluid; that IgG2 transfer through both barriers is a result of passive diffusion only and that the content of efferent lymph is strongly influenced by IgG1, IgM and IgA in the mammary tissue, brought to the lymph node by afferent lymph.
Highlights
The first hours after antigen stimulation, interactions occur influencing the outcome of the immunological reaction
The most rapid increase of Igs was observed in afferent lymph, resulting in significantly higher concentration of each Ig isotype, except for IgG2, in afferent than in efferent lymph at postinfusion hour (PIH) 2, contrary to before challenge
The transfer of Igs through the endothelium appeared to be merely a result of diffusion while the transfer through the epithelium and the Ig concentrations in milk seemed to be more influenced by selective mechanisms and local sources, respectively
Summary
The first hours after antigen stimulation, interactions occur influencing the outcome of the immunological reaction. For studies of tissue reactions over time when repeated sampling is desirable, it appears more suitable to examine interstitial fluid that can be sampled frequently after it has entered the collecting vessels of the peripheral (afferent) lymphatic system in the tissue, through application of a semi-permanent catheter This method was used in the present investigation parallel to examination of efferent lymph, leaving the local supramammary lymph nodes and analysis of milk. It enabled us to follow the inflammatory response along the entire pathway from the mammary milk compartment, through the interstitial space in the tissue, the afferent lymphatics and the local lymph node; a route where the immune events are initiated and of significant immunological interest It further made it possible to separately study the transfer of various components through, on one hand the mammary endothelium and on the other hand the mammary epithelium
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