Monocyte-enriched preparations derived from peripheral blood leukocytes of atopies were probed via a cocktail comprising peroxidase-conjugated (Fab¹)₂ fragments of two monoclonal antibodies against human IgE. Reaction product indicative of intracellular IgE was identified by electron microscopy in both large and small vacuoles, and at high magnification exhibited a characteristic granular deposition pattern consistent with highly concentrated (perhaps insolublized) material. IgE-containing vacuoles were observed with comparable frequency to those containing IgG, despite the > 10,000-fold relative excess of the latter in serum suggesting highly selective uptake of IgE by the monocytes. These results are similar to those reported recently for IgA in human milk macrophages.

Peripheral blood mononuclear B cells from 6 rye pollen-allergic patients, with no consistent perennial symptoms, were isolated before (July), during (October) and after (February and May) the pollen season. The T-depleted cells were fractionated on a discontinuous percoll density gradient and the B cell fractions, together with unfractionated B cells, incubated in vitro for quantitation of spontaneous synthesis of rye pollen-specific IgE. Markedly higher levels of IgE were synthesised by the fractions, as opposed to unfractionated B cells. The low-density fraction (B₅) contributed most towards synthesis in the pollen season and the denser B₆ cells in the pre- and post-pollen season. All low-density B cell fractions (B_1-3–B₅) and some high-density fractions contained large but variable amounts of preformed specific IgE which was retained, even in the absence of de novo synthesis in vitro, during the post- and pre-pollen season. Since only a fraction of this preformed IgE escaped into culture supernatants the contribution of preformed IgE to in vitro IgE synthesis in general may require reappraisal.

Summary Fractionation by Percoll density cetrifugation 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 ceils 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 intraceilular 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.

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Peripheral-blood leucocytes from Dermatophagoides pteronyssinus- and/or Lolium perenne-allergic patients produce in vitro histamine-releasing factor (HRF) in an allergen-specific and concentration-dependent relationship. Maximum production of HRF occurred in cultures containing as little as 10–100 pg/ml crude allergen extract, although a second peak occurred at higher concentrations (10–100 μg/ml). While HRF was detectable in 1-hour cultures, maximal production required 24 h in culture. In contrast, HRF induced by streptokinase/streptodornase (SK/SD) was generally maximal after 1 h. Allergen-induced HRF production was almost exclusively associated with monocytes and B cells. In contrast, peripheral-blood T cells were the major source of induced HRF production in cultures containing SK/SD. Histamine-releasing cytokines are apparently produced by different cell populations, the activation of which may be dependent upon the characteristics of the stimulating antigen.