Antigen-Receptor Interactions in the Induction of B-Lymphocyte Unresponsiveness. In: Arber W, Henle W, Hofschneider PH, Humphrey JH, Klein J, Koldovský P, Koprowski H, Maaløe O, Melchers F, Rott R, Schweiger HG, Syruček L, Vogt PK, editors. Current Topics in Microbiology and Immunology. Berlin: Springer Berlin Heidelberg; 1977. pp. 31-68. [DOI: 10.1007/978-3-642-66800-5_2]

Tolerogenic or immunogenic activity of hapten-conjugated polysaccharides correlated with cellular localization

Dinitrophenylated (DNP) conjugates of Ficoll, hydroxyethyl starch, levan, dextran, type 3 pneumococcal capsular polysaccharide SIII, pectin, alginic and hyaluronic acid at various epitope densities were tested for their capacity to inhibit secondary IgG anti-DNP antibody responses using an in vivo transfer system. Some aminobenzylarsonate conjugates were examined similarly. Conjugates of the acidic polysaccharides were markedly more effective than those of uncharged polysaccharides. Conjugated with high epitope densities were particularly tolerogenic. DNP conjugates of Ficoll and hydroxyethyl starch elicited prolonged IgM responses over a wide dose range, and there are indications in the literature that conjugates of dextran do likewise. All the polysaccharide conjugates, labeled with radioiodine, persisted in the body for long periods (half-lives 8.5--63 days), and all were cleared rapidly from, but remained detectable in the blood for many days. Gross tissue distributions varied markedly from one conjugate to another, and autoradiography revealed unexpected differences in cellular localization. Despite substantial retention in the liver, some uncharged polysaccharides were localized only in parenchymal and not in Kupffer cells. In the spleen, only the acidic polysaccharides were predominantly localized in red pulp macrophages, and the neural polysaccharides were detectable exclusively, and in the case of Ficoll, hydroxyethyl starch and some dextrans very intensely in macrophages of the marginal zone of the white pulp. It is suggested that retention of thymus-independent antigens in marginal-zone macrophages favors, whereas trapping in red-pulp macrophages diminishes immunogenicity, and that tolerogenic effectiveness depends upon a balance between tolerization of B cells by free antigen and stimulation by antigen presented by marginal-zone macrophages. The distinction between functionally different macrophages in the spleen is elaborated in the following report.

Different macrophage populations distinguished by means of fluorescent polysaccharides. Recognition and properties of marginal-zone macrophages

Fluorescent conjugates of hydroxyethyl (OEt) starch of Ficoll are selectively ingested and retained in vivo by spleen marginal-zone (MZ) and lymph node marginal-sinus macrophages of mice, whereas similar conjugates of type 3 pneumococcal capsular polysaccharide (SIII) are generally retained by macrophages (Kupffer cells, histiocytes, macrophages of spleen, lymph nodes, bone marrow and peritoneal cavity). MZ and other macrophages are readily identifiable by fluorescence after injection in vivo of OEt starch and SIII labeled with tetraethylrhodamine isothiocyanate and fluorescein isothiocyanate. Collagenase digestion was required for recovery of intact MZ macrophages from spleen in single cell suspensions and for maximum yields of other macrophages. MZ macrophages are larger and morphologically distinct from other macrophages, but resemble them in respect of EA, EAC receptors and acid phosphates and nonspecific esterase content and are equally radio-resistant. The appear normal in CBA/N nude and in beige mice. Freshly isolated MZ macrophages in suspension have adherent lymphocytes, dispersible by EDTA treatment, with B but not T cell markers. It is suggested that selective adherence to MZ macrophages is a factor in determining B cell traffic. MZ macrophages did not have demonstrable surface I-A or I-EC antigens. Only 4--8% of other spleen macrophages freshly isolated by collagenase treatment expressed I-A in the same preparation, whereas 35% of other cells (lymphocytes and blasts) reacted with monoclonal anti-I-A and anti-I-EC. After adherence to glass or plastic, 40% or more red-pulp, but not MZ macrophages, became I-A-positive. When taken from mice recently restimulated with sheep erythrocytes, half the red-pulp macrophages expressed I-A even before adherence. The relation of MZ to other macrophages is not known. However, their properties are consistent with the demonstrated ability of thymus-independent antigens selectively taken up by these cells to elicit long-lasting IgM antibody responses by direct interaction with B cells. The unexpected observation that only a small proportion of spleen macrophages freshly isolated from unstimulated mice had detectable surface I-A, but that this proportion was much increased after attachment to plastic, is discussed in relation to the possibility that macrophages do not express surface Ia antigens unless they have been stimulated.