Antigen uptake and presentation by ovine afferent lymph dendritic cells
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1994Author
Coughlan, Susan Nicola
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Abstract
Dendritic cells (DC) are accessory cells distributed throughout non-lymphoid and
lymphoid tissues, and also found in the blood and afferent lymph. These cells represent
1-10% of the leucocytes in ovine afferent lymph, and can be purified using
pseudoafferent cannulation techniques. DC are essential as accessory cells for the
initiation of primary immune responses, and are also the most effective antigen
presenting cells for activation of T cells in the secondary response. However, the
mechanisms underlying the potent accessory capability of DC are currently poorly
understood. The aims of this thesis were to characterise DC surface markers and Fc
receptor expression in primary and secondary immune responses, and to investigate the
effect of enhanced antigen uptake via DC Fc receptors on T cell activation.
The phenotype of DC from the afferent lymph of sheep was investigated by flow
cytometry. MHC class I, class II and CD1 were observed at high levels on the DC
surface, while staining for immunoglobulins was variable. Cells obtained from the
afferent lymph of primed sheep on antigen challenge in vivo showed pronounced and
rapid modulation of surface markers, which may be required for processing and
presentation of antigen and migration to the draining lymph node. Further characterisation of DC demonstrated staining with polyclonal antisera to
peptides of the bovine Fc receptor Type I for IgG. Western blot analysis of DC lysates
identified bands of the correct sizes for the Type I and II Fc receptors for IgG,
suggesting that both are expressed by ovine afferent lymph DC. Functional studies were carried out to investigate the role of Fc receptors for IgG in the
uptake and presentation of antigen by DC. Specific antibody greatly increased the
response of CD4+ T cells to substimulatory concentrations of antigen presented by DC,
depending on the antigen/ antibody ratio. F(ab')2 portions of specific antibody and
intact irrelevant antibody were completely ineffective. These results suggest enhanced
presentation of antigen by DC following the uptake of immune complexes via Fc
receptors. Similar results, although with a smaller degree of potentiation, were obtained
using unfractionated peripheral blood mononuclear cells. using unfractionated peripheral blood mononuclear cells.
Fc receptors on DC would be important in secondary responses in vivo, in which
specific antibody of IgG isotype is present. The potentiation of T cell activation may
also play a role in diseases in which immune complexes are presented by DC.