Interleukin-1 receptor expression by ovine afferent lymph dendritic cells: response to secondary antigen challenge

Interleukin (IL)-1 is thought to enhance the function of antigen presenting cells of the dendritic cell lineage. To investigate the interaction of IL-1 and dendritic cells recombinant ovine IL-1 alpha and IL-1 beta have been used to determine IL-1 receptor (R) expression on fresh dendritic cells (ALDC) collected from cannulated sheep pseudoafferent lymph ducts, both prior to and in response to localized ovalbumin challenge. Resting ovine ALDC express approximately 510 IL-1R per cell for IL-1 alpha (Kd approximately 30 pM) and approximately 350 IL-1R/cell for IL-1 beta (Kd approximately 160 pM). Saturation binding and in situ analyses show an initial transient but dramatic increase in IL-1 alpha binding to ALDC by 4 h in response to ovalbumin challenge of primed sheep. Maximal IL-1R expression, reaching > or = 21700 IL-1R/cell for IL-1 alpha detected by around 48 h, was followed by a gradual return to resting level by 8 days post challenge. Fewer than 0.5% of resting ALDC expressed IL-1R but at least 5% of ALDC bound IL-1 alpha after ovalbumin challenge. There was no evidence of specific up-regulation of receptors for IL-1 beta on these cells. Fresh ovine alveolar macrophages, used as a positive control for specific IL-1R expression, were found to express approximately 2600 sites/cell for IL-1 alpha (Kd approximately 56 pM) and 16,500 sites/cell for IL-1 beta (Kd approximately 4.6 pM). In view of the differing IL-1 binding characteristics displayed by the receptors on the two cell types, it is postulated that afferent lymph dendritic cells and macrophages are not expressing the same form of IL-1R.