The consequences of the intracellular retention of pathogen-derived T-cell-independent antigens on protein presentation to T cells

Intracellular pathogens can be considered as particulate antigens chemically composed of a complex mixture of T-cell-dependent antigens (TD) (peptides and proteins) and T-cell-independent antigens (TI) (glycolipids and complex polysaccharides). A large range of saccharides (from oligosaccharides to complex polysaccharides) derived from pathogenic microorganisms are being isolated and characterized. They are currently implicated in signaling systems and concomitant host-parasite relationships. However, there are not many structure-function relationships described for these pathogens. This is particularly true of polysaccharides. In this report we have reviewed the role of defined TI antigens in the processing and presentation of defined TD antigens to specific T cells by antigen-presenting cells (APC). We also considered the importance of some of the chemical characteristics shared by different carbohydrates implicated in the inhibition of antigen presentation. These findings are discussed in relation to the clear immunopathological consequences of long retention periods of complex carbohydrate molecules derived from intracellular parasites inside certain APC and the absence of antigen presentation impairment in physiological situations such as the removal of senescent or damaged red blood cells by splenic macrophages or intracellular accumulation of carbohydrates in colostrum and milk macrophages during lactation.

Total IgE levels in human colostrum

The aim of this study was to assess the total IgE levels in the supernatants and cellular components of colostrum from atopic and nonatopic mothers. Immunoglobulin E protein was detected in 34/39 milk samples, with a median level of 0.3 microgram/l. In 13 mothers, IgE protein was also detected in the cellular fraction of colostrum, with a median level of 0.13 microgram/l. Of the total IgE content in breast milk, 5-12% was transported intracellularly. The total IgE antibody levels were similar in both milk supernatants and cells from atopic and nonatopic mothers. There was a strong relationship between total IgE antibody levels in serum and in breast milk (r = 1.0, P < 0.001), suggesting that IgE antibodies were passively transported from blood into breast milk. The levels of total IgE in human milk are probably too low to have a significant effect on the regulation of the IgE antibody levels in the neonate.

Seasonal variation of IgE synthesis in vitro by human peripheral blood mononuclear cells

Seasonal variations in IgE antibody synthesis in vitro were studied in cultures of blood mononuclear cells (MNC) from 11 pollen allergic individuals. The IgE levels were significantly higher in two summer seasons than in the winter and spring between them. Net synthesis was confined to the summer in all but one of the patients. All the IgE in the cultures outside the pollen season represented preformed IgE which was present mainly (59%) in the monocyte fraction. Thus, preformed IgE seems to persist in monocytes at times when there is little de novo synthesis of IgE.

In vitro synthesis of IgE by human peripheral blood leucocytes: VI. Seasonal variations in synthesis of rye pollen (Lolium perenne) specific IgE

Fractionation by Percoll density centrifugation of peripheral blood leucocyte cells, from atopic subjects with seasonal hay fever, unmasked IgE-B cell populations whose individual capacities to synthesize IgE in vitro were obscured in cultures of unfractionated B cells. B cell cultures from all six subjects in the study released rye pollen-specific IgE during the 6 days of culture, but actual synthesis was significant only in October, the pollen season. Synthesis in October occurred most frequently in cultures of mature, low density B cells, which generally responded to the addition of autologous T cells with enhanced synthesis (T-help). T-help was also found for high density B cells in the mid-winter (July) cultures. Total IgE synthesis in vitro demonstrated a less seasonal relationship, although it tended to be maximal for low density B cell cultures in October and for high density B cells in May. All B cell cultures contained preformed total and rye-specific IgE antibody which persisted throughout the pre- and post-pollen seasons, particularly in the low density B cell fractions, even in the absence of de novo synthesis. Moreover, the intracellular levels of rye pollen-specific IgE antibody were often higher in the winter than in the peak of the pollen season. The relevance of this preformed IgE remains to be established.