Ontogeny of murine I-Ak antigens in tissue of nonlymphoid origin

Immunobiology of liver dendritic cells

Dendritic cells (DC) are rare, bone marrow-derived antigen-presenting cells that play a critical role in the induction and regulation of immune reactivity. In this article, we review the identification and characterization of liver DC, their ontogenic development, in vivo mobilization and population dynamics. In addition, we discuss the functions of DC isolated from liver tissue or celiac lymph, or propagated in vitro from liver-resident haemopoietic stem/progenitor cells. Evidence concerning the role of DC in viral hepatitis, liver tumours, autoimmune liver diseases, granulomatous inflammation and the outcome of liver transplantation is also discussed.

In vivo class II transactivator expression in mice is induced by a non-interferon-gamma mechanism in response to local injury

BACKGROUND

Tissue injury induces MHC class II expression, which could be important in the recognition of that tissue as an allograft. The class II transcriptional activator (CIITA) is the major regulator of basal and induced MHC class II expression and is essential for antigen presentation. The role of CIITA in the induction of class II by tissue injury is unknown. In this study, we examined CIITA induction in the course of acute ischemic or toxic renal injury in mice, including the role of interferon (IFN)-gamma and of the transcription factor, interferon regulatory factor (IRF)-1.

METHODS

Kidneys were injured by ischemia or by gentamicin toxicity and were then studied for changes in gene expression using Northern blot, reverse transcriptase-polymerase chain reaction, radioimmunoassay, and tissue staining. We compared wild-type (WT) mice to IFN-gamma knockout (GKO) or IRF-1 knockout mice.

RESULTS

Ischemic injury induced CIITA and class II expression in the kidney, in WT and GKO mice. Gentamicin injury also induced both CIITA and class II expression, independent of IFN-gamma, in WT and GKO mice. After ischemic injury, the induction of class II protein levels and CIITA and class II mRNA levels were induced, to a lesser degree, in IRF-1 knockout mice.

CONCLUSIONS

These data indicate that CIITA is induced by tissue injury, and probably accounts for class II induction during tissue injury. CIITA induction by injury is largely IFN-gamma independent but requires IRF-1. The similarities of the pattern of CIITA and class II induction in ischemic and toxic injury suggest that this is a stereotyped response of injured tissue and not a consequence of a particular mechanism of injury.

Neonatal tolerance induction in the thymus to MHC-class II-associated antigens. II. Significance of MHC antigens in anti-Mls tolerance

Specificity of anti-Mlsa tolerance induced in BALB/c (H-2d, Mlsb) neonates was investigated by a popliteal lymph node (PLN)-swelling assay for the local graft-versus-host (GVH) reaction by injecting tolerant thymus cells into the footpads of several types of F1 hybrid mice. When thymus cells were obtained from 1-week-old normal BALB/c, they evoked enlargement of PLNs of (BALB/c X DBA/2)F1 (H-2d, Mlsb/a) [CDF1] recipients and of other hybrid recipients, heterozygous in Mlsa,c,d alleles, irrespective of the major histocompatibility complex (MHC) haplotypes. The same thymus cells did not cause the response in MHC-heterozygous F1 hybrids when the hybrids were homozygous in Mlsb, identical with BALB/c mice. Therefore, the PLN response to Mls antigens, known to be closely associated with MHC-class II antigens, was not directed to the class II antigens themselves. This enabled us to examine the effects of MHC on tolerance induction to the Mls antigens. When BALB/c neonates were injected with CDF1 bone marrow cells, complete tolerance to Mlsa-H-2d antigens of CDF1 cells was induced in the thymus, while responsiveness to Mlsa antigens in the context of H-2k and H-2b antigens, was not affected. This indicates MHC-restriction of neonatal tolerance to Mls antigens. Furthermore, when Mls and H-2-heterozygous (BALB/c X AKR)F1 (H-2d/k, Mlsb/a) bone marrow cells served as the tolerogen, thymus cells of BALB/c neonates were also tolerized to Mlsa-H-2k antigens as well as to Mlsa-H-2d antigens, which suggests the involvement of MHC, probably class II antigens of tolerance-inducing cells.

Ontogeny of Ia-positive and Thy-1-positive leukocytes of murine epidermis

Murine epidermis harbors 2 populations of dendritic leukocytes: Langerhans cells (LC) and Thy-1-positive dendritic epidermal cells (Thy-1 +DEC). In the adult mouse these cell types are morphologically distinct and display highly characteristic phenotypes. LC bear Ia-antigens and a group of markers typical for mononuclear phagocytes: Fc- and C3bi-receptors, macrophage-specific antigen F4/80, and membrane ATPase. Thy-1 +DEC, in contrast, lack these markers but express high levels of Thy-1 and asialo-GM1 (asGM1) antigen. Since LC and Thy-1 +DEC share a common origin from the bone marrow we expected to gain insight into their relationship by studying their ontogenetic development. Epidermal sheets from fetal and newborn C3H/He and C57B1/6 mice obtained at defined ages from day 17 of gestation up to day 30 of postnatal life were monitored for the emergence of the above-mentioned markers for LC and Thy-1 +DEC. In double-labeling experiments LC markers were first detected by visualizing the monoclonal antibodies by a sensitive triple-layer rhodamine-immunofluorescence technique; in a second step, after appropriate blocking procedures, Thy-1 and asGM1 antigens were demonstrated by direct and indirect immunofluorescence. We found that in fetal epidermis, only few cells expressed either Thy-1 or Ia (4 and 1 cells/mm2, respectively, on day 18 of gestation). The bulk of Thy-1 +DEC and Ia +EC appeared only after birth. Adult proportions of Thy-1 +DEC and Ia +EC were reached at around 1 month of postnatal life. In contrast, all the other LC markers were expressed on a substantial number of fetal dendritic cells (280 cells/mm2 on day 18 of gestation), indicating the presence of phenotypically immature Ia-negative LC in fetal epidermis. By day 4 of postnatal life all F4/80 +EC and ATPase +EC (i.e., LC) had acquired Ia-antigens. Surprisingly, LC also bore asGM1 antigens, which in the adult epidermis are strictly confined to Thy-1 +DEC, up to day 5 of postnatal life. Thus, LC in fetal and early newborn epidermis are not yet fully differentiated. As they differentiate, they acquire Ia antigens and lose asGM1 antigens. In contrast, a phenotypically immature Thy-1 +DEC population could not be traced with the markers used. Thy-1 +DEC appear to be characterized by a stable phenotype (Thy-1+/asGM1+) throughout their lifetime.

Expression of interleukin 2 receptor on murine fetal thymocytes

Rat monoclonal antibodies AMT-13, 3C7 and 7D4 which react to the mouse interleukin 2 (IL 2) receptors were used to define cell populations with the putative IL 2 receptors in the mouse thymus as a part of series of investigations to elucidate the mechanism of intrathymic cell proliferation and differentiation. With freshly dissociated cells from the thymus of 15 gestational days, the anti-IL 2 receptor monoclonal antibodies (anti-IL 2 receptor) reacted with about half of them. The proportion of the reactive cells decreased rapidly thereafter till birth as the numbers of thymus cells expanded. The antibodies reacted with only two to three percent of thymic cells from newborn mice and less than one percent of cells from adult thymus. Through the gestational period, the fetal liver cells did not react with the antibodies. When the thymus cells at early gestational days were subjected to a two-color analysis, one for the anti-IL 2 receptor and the other for anti-Thy-1 or anti-asialo GM1, by a fluorescence-activated cell sorter, it was found that the majority (up to 80%) of anti-IL 2 receptor-reactive cells (IL 2 receptor-positive cells) was also reactive with anti-Thy-1. Some of the IL 2 receptor-positive cells but Thy-1-negative cells reacted with anti-asialo GM1, a marker of the immature thymocytes. Immunohistochemically, the IL 2 receptor-positive cells were found mainly in the subcapsular area and in the border region of cortex and medulla. Collectively, these results suggest that the pre-T lymphocytes are stimulated immediately after their arrival to the thymus from the stem cell source such as fetal liver and bone marrow and are driven into the proliferation via the IL 2 receptor system.

Differential tissue distribution and ontogeny of DC-1 and HLA-DR antigens

The tissue distribution and the ontogeny of DC-1 antigens have been investigated and compared with those of HLA-DR antigens. Indirect immunofluorescence (IIF) staining of surgically removed normal tissues from adults with the monoclonal antibody (MoAb) BT3.4 has detected DC-1 antigens in tissues of various embryologic origin. The tissue distribution of DC-1 antigens is more restricted than that of HLA-DR antigens, as the former are not detected in duodenal epithelium, colon mucosa, and ductal mammary gland epithelium. In fetuses up to 26 weeks of age, DC-1 antigens were detected only on cortical and medullary thymic dendritic cells with an anatomic distribution similar to that of reticuloepithelial cells and in endothelial cells of the small intestine. At this stage of intrauterine life, HLA-DR antigens have already reached their full tissue distribution. The tissue distribution and the ontogeny of DC-1 antigens resemble those of their murine counterparts, i.e., the I-A antigens.