B cell differentiation in sheep

The ileal Peyer's patch (IPP) of lambs is a region of intense lymphopoiesis and B cell development. Monoclonal antibodies against ovine lymphocyte antigens have been used to characterise the IPP lymphocyte. Three murine monoclonal antibodies against ovine IgM, IgGi 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.

The ileal Peyer's patch (IPP) of lambs is a region of intense lymphopoiesis and B cell development. Monoclonal antibodies against ovine lymphocyte antigens have been used to characterise the IPP lymphocyte. Three murine monoclonal antibodies against ovine IgM, IgGi 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 lipopolysaccharide (LPS) and interleukin 2 (IL2). Proliferation is inhibited by rabbit anti-sheep Ig antibodies. Using an ELISA for Ig, it has been posible 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 en 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 inci-ease are discussed.