B cell differentiation in sheep

• Main Author: Jones, Philip Anthony
• Published: University of Edinburgh 1988
• Subjects: 571.96
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.653124

The ileal Peyer's patch (IPP) of lambs is a region of intense lymphopoiesis and B cell development. Monoclonal antibodies against ovine lymphoctye antigens have been used to characterise the IPP lymphocyte. Three murine monoclonal antibodies against ovine IgM, IgG1 and Ig light chain were produced and are described fully. IgM and MHC class II antigens are expressed on the vast majority of IPP cells whilst cells bearing other serum Ig isotypes and T cell antigens are rare. A novel Ig molecule appears to be coexpressed with IgM, it is proposed that this is the ovine equivalent of IgD. IPP cells can be induced to proliferate and differentiate when cultured with lipo-polysaccharide (LPS) and interleukin 2 (IL2). Proliferation is inhibited by rabbit anti-sheep Ig antibodies. Using an ELISA for Ig, it has been possible to quantitate Ig synthesis and secretion. Mean cellular Ig increases greater than 25-fold during differentiation. High-rate secretion begins 4 days after initiation of culture and is virtually complete by day 7. As IPP B cells differentiate to IgM secretion, membrane Ig is rapidly lost so that by day 6, only 15% of cells express Ig on their surfaces. Changes in MHC class II antigens were also studied. Surface expression of MHC class II molecules doubled by 24 hours and slowly declined to resting levels as differentiation proceeded. A large increase in cytoplasmic MHC class II content was noted on day 3. The reasons for this increase are discussed. Kinetic studies suggest that IL2 responsiveness is acquired approximately 20 hours after activation by LPS. The concentration required to give half maximal Ig secretion is 125 pM indicating that the interaction between IL2 and its receptor is one of high affinity. During differentiation, the cells enlarge and show an increase in the cytoplasmic:nuclear ratio. The formation of extensive rough endoplasmic reticulum and additional mitochondria is indicative of the functional changes occurring. This is the first description of a sheep B cell differentiation assay. It is proposed that this system is a suitable model on which to base further studies into the molecular biology of sheep Ig genes, Ig isotype switching and lymphokines and their receptors.