E. A. Döpp

The heterogeneity of mononuclear phagocytes in lymphoid organs: distinct macrophage subpopulations in the rat recognized by monoclonal antibodies ED1, ED2 and ED3.

In the present study, a set of three monoclonal antibodies is described, each of which recognizes cells of the monocyte-macrophage lineage in the rat. The tissue distribution, in particular in lymphoid organs, of each of the three monoclonals is determined by immunoenzyme histochemistry on cryostat sections, as well as on cell suspensions. Results show that ED1 recognizes a cytoplasmic antigen in monocytes and in most macrophages, free and fixed. ED2 and ED3 recognize membrane antigens of tissue macrophages, discriminating between distinct subpopulations of macrophages, each with a characteristic localization in the compartments of lymphoid organs. No other cell types except cells of the mononuclear phagocyte system are positive for any of the three monoclonals. Possible relations between the macrophages recognized by this set of monoclonals and dendritic cells are discussed.

The ontogenetic development of the follicular dendritic cell

SummaryAfter intravenous injection of horseradish peroxidase (HRP)-anti-HRP complexes in 21-day-old rats, complex trapping occurs on reticulum cells, forming the stroma of primary follicles of spleens. After intravenous injection of the same complexes in young adult rats (48 days old), trapping occurs on characteristic follicular dendritic cells (FDCs) located in well-developed germinal centers. These results strongly suggest that the follicular dendritic cell originates from a reticulum cell.

Ontogenetic aspects of immune-complex trapping in the spleen and popliteal lymph nodes of the rat

SummaryAn ontogenetic approach was used to obtain information about the relation between structure and function of lymphoid tissues. In particular the development of the capacity to trap immune complexes was studied in relation to the development of the lymphoid compartments. For this purpose isologous horseradish (HRP)-anti-HRP complexes were injected into neonatal rats, and their fate was studied in the spleen and popliteal lymph nodes. Immune-complex trapping occurred as soon as primary follicles could be recognized; without follicles no trapping was observed. Several explanations for this simultaneous development of trapping capacity and follicular structure are discussed.

The postnatal development of cell populations in the rat popliteal lymph node

SummaryThe postnatal development of the various cell populations in the rat popliteal lymph node was investigated applying enzyme-histochemical and immunohistochemical techniques. From birth, T-lymphocytes and interdigitating cells were demonstrable. During the development of the young lymph node, T-lymphocytes of the helper phenotype outnumbered the T-cells with a suppressor phenotype; they account for approximately 70% and 30% of all T-lymphocytes, respectively. At the very first day of postnatal life, post-capillary venules were already present. B-lymphocytes occurred later than T-cells during ontogeny; they were found on the second day after birth, most of them being IgM- or IgG-bearing lymphocytes. The first primary follicles occurred at day 18 and contained principally membrane-stained IgM cells and, to a lesser extent, membrane-stained IgG cells. The appearance of follicular dendritic cells correlated with the formation of primary follicles. With respect to the macrophages, it appeared that the ED1- and ED3-positive subpopulations were present with a similar distributional pattern as seen in adults, but in considerably lower numbers. The expression of ED2, however, showed a sudden increase in the third week of life. Findings of the present study are discussed in relation to those obtained in other investigations dealing with the ontogenetic development of lymphoid organs.

Properties of mouse CD40: differential expression of CD40 epitopes on dendritic cells and epithelial cells

In this study we describe the tissue distribution of mouse CD40 using two monoclonal antibodies (mAb) against different epitopes of the molecule. In lymphoid tissues CD40 was expressed by B lymphocytes. Most B cells in typical B‐cell compartments were CD40‐positive, including germinal centre B cells. Interestingly, the two CD40 epitopes were differentially distributed on subpopulations of dendritic cells and epithelial cells. The 3/23 mAb, but not 3/3, recognized interdigitating dendritic cells (IDC) in lymph nodes, spleen and thymus. Langerhans cells were CD40 negative. In contrast, epithelial cells in the thymus and some other tissues (e.g. skin) were stained with the 3/3 mAb, but not with the 3/23 mAb. The expression of CD40 on dendritic cells and epithelial cells is in agreement with earlier findings in humans. Our data also demonstrate that different epitopes of CD40 are differentially expressed on dendritic cells and epithelial cells. This suggests the existence of different forms of CD40, that are expressed in a cell‐type‐specific fashion.

Immunological Characteristics of Milky Spots in the Omentum of Rats

In the rat model we have clearly shown In the past that the diversity of cytochemically heterogeneous populations of macrophages is best explained by stage of maturation differentiation of cells belonging to one lineage(1) in the sequence monocyte (or exudate macrophage) — exudate-resident macrophage — resident macrophage, the dynamics being related to the state of inflammation induced (2,3). Our earlier studies on milky spots In the omentum Indicated that they are a source of the free peritoneal macrophages as judged by the maturation pattern based on morphology (4) and cytochemistry (5). Moreover, precursor cells as promonocytes may settle and proliferate in milky spots and so locally generate as a pool of monocytes and macrophages. Interestingly in the milky spots the more immature macrophages were found inside and the mature resident macrophages outside, indicating their maturation route. These results were later confirmed by others (6,7).

Transport of immune complexes from the subcapsular sinus into the lymph node follicles of the rat

To study the mode of transport of immune complexes from the subcapsular sinus into the follicles of draining popliteal lymph nodes, horse radish peroxidase (HRP)-anti HRP was injected in rat footpads. Within six minutes, complexes were already present in the subcapsular sinus freely or attached to the plasma membrane of different types of cell including cells forming the stroma. A few minutes later, complexes were also seen in the deeper part of the outer cortex, and after two hours they had reached the periphery of the follicles. They were always seen scattered between lymphoid and non-lymphoid cells. After one day, complexes were present on well-developed follicular dendritic cells. After injection of HRP, no localization of this antigen was observed in the deeper part of the outer cortex including the follicles. These results strongly suggest that HRP-anti HRP complexes are passively transported through the outer cortex into the follicles where they are trapped and retained by follicular dendritic cells.

Regeneration of splenic tissue after autologous subcutaneous implantation: Homing of T- and B- and Ia-positive cells in the white pulp of the rat spleen

SummaryThe localization of T-and B lymphocytes and interdigitating cells (IDC) was investigated during the regeneration process of splenic implants. For this purpose a two-step immunoperoxidase technique was used to visualize T-cell antigen, immunoglobulins and Ia-antigen on cryostat sections. The specific localization of the repopulating lymphocytes occurred simultaneously with the development of non-lymphoid elements characteristic for the different compartments of the white pulp, i.e., the periarteriolar lymphocyte sheaths (PALS) and follicles. The marginal zone (MZ) developed after the PALS and primary follicles, but before germinal center reactions were found. During ontogeny, however, the development of a broad MZ precedes the formation of follicles. This difference in sequence of events is discussed.

ONTOGENY OF MACROPHAGES AND DENDRITIC CELLS OF THE RAT

Earlier studies on the ontogeny of macrophages have demostrated that the immunological immaturity of newborn rodents is at least in part due to the immaturity of the macrophage system (1,2). In particular the capacity of macrophages to present antigen and thus induce an adequate immune respons was impaired in neonates as compared to adults (13,19,21), which appeared to be due to a low number of la-positive antigen presenting cells (15,20). A considerable number of studies are now available on the ontogenetic development of antigen presenting cells in the different lymphoid organs as thymus (10,12), gut and gut-associated tissue(17,25,26), spleen (7,11) and lymph node (24) or in cell suspensions of these organs (14,16). In these studies, the antigen presenting cells, in particular the interdigitating cells (IDC, in tissues) respectively dendritic cells (DC, in cell suspensions) were studied using either their expression of la-antigen or their antigen presenting capacity as characteristic.

Immune-complex-trapping cells in the spleen of the oriental fire-bellied toad, Bombina orientalis

SummaryThe spleen of the oriental fire-bellied toad, Bombina orientalis, consists of well-developed white pulp, separated from the lymphocytic marginal zone by the connective tissue boundary layer. Injection of peroxidase-conjugated rabbit anti-peroxidase revealed that these immune complexes were localized on the surface of acid-phosphatase-positive and non-specific-esterasepositive cells in the white pulp. The majority of immunecomplex-trapping cells were present around the blood vessels. Cell processes of some of these cells penetrated into the wall of blood vessels. The significance of the present findings is discussed with respect to the evolution of immune-complex-trapping cells in the spleen.