Analysis of graft-versus-host disease in Syrian hamsters. IV. The refractory state and immunologic competence.

The so-called refractory state, one sequela of acute graft-versus-host disease, has been studied in adult (CB x MHA)F(1) hybrid Syrian hamsters inoculated with sublethal numbers of MHA-anti-CB lymphoid cells. Intracutaneous challenge of these animals with 200 million MHA-anti-CB lymphoid cells after the acute syndrome subsided failed to evoke epidermal necrolysis, whereas a similar challenge administered to normal F(1) recipients invariably resulted in lethal epidermolysis. Moreover, the gradual attrition of lymphatic tissues in these hosts and their fading capacity to display adequately immune lymphocyte transfer reactions in the skin coincided with increasing evidence of host refractoriness, suggesting a causal interrelationship. It was possible to circumvent refractoriness by challenging these animals intracutaneously with MHA-anti-CB cells if: (a) the hosts had been lethally irradiated and reconstituted with F(1) hematopoietic cells, or (b) the intracutaneous inocula contained admixed F(1) lymphoid cells. This evidence provides additional support for the hypothesis that in GVH disease donor lymphocytes attack primarily host lymphoid cells bearing offending homologous antigens. The GVH process can continue so long as these lymphocyte-bound antigens persist within the host, and will abate only as the aggregate host lymphatic mass is effectively destroyed (hamsters) or its antigenic determinants are masked by isoantibodies (rats, mice, man?). At this point, insufficient target tissues remain for rechallenge to incite significant recrudescence of the disease.

T cells recognize minor histocompatibility antigens on H-2 allogeneic cells.

B10.A animals were rendered tolerant to B10.M spleen cells by injection of (B10.A X B10.M)F1 cells into neonates. Adult animals accepted B10.M skin grafts and failed to generate cytotoxic effector cells in vitro against B10.M H-2 antigens. In vivo inoculation of tolerant animals with A.CA spleen cells, followed by in vitro challenge with similar cells, resulted in the generation of cytotoxic effector cells that had specificity for the A strain minor histocompatibility (H)-antigens in the context of the H-2f haplotype. If these animals were boosted in vitro with A strain spleen cells, cross-priming could be demonstrated, whereby the cytotoxic effect was restricted by the H-2a haplotype. These data indicate that at least two sets of T cells co-exist in tolerant animals, one capable of recognizing antigens in the context of the host H-2 haplotype, and the other able to recognize antigens in the context of the tolerated H-2-allogeneic haplotype. Because tolerant animals inoculated with A-strain spleen cells in vivo and boosted in vitro with A.CA spleen cells failed to generate a cytotoxic effect against A.CA, it is unlikely that minor H-antigens need to be processed by host lymphoreticular cells.

Influence of splenectomy on first set rejection reactions of C57BL/6 females to male skin isografts.

The tempo with which C57BL/6 females reject male skin isografts is determined in part by the immunogenicity of the H-Y antigen and in part by the capacity of the host to respond immunologically. Our studies indicate that the spleen plays an important role in determining the briskness of the rejection process in that splenectomy 7-30 days before grafting with male skin significantly shortens the survival time. The results of reconstitution experiments suggests that a population of cells is present in spleens of normal, but not specifically sensitized, females which can restore the conventional first set reaction in splenectomized females. It is inferred that this resident population normally operates in spleen-intact females to delay the development of specific effector responses. Lymphoid cells from H-Y antigen-sensitized, splenectomized females failed to evoke graft-vs.-host responses in males whereas similar cells from females with spleens intact did possess graft-vs.-host potential.

Haptens can serve as surrogate transplantation antigens in a manner that demonstrates H-2 restriction of graft rejection.

Hapten-immune mice are capable of rejecting syngeneic skin grafts that are derivatized with the relevant hapten, but only if the hapten is applied while the graft is "healing in." This model system was used to demonstrate that the hapten-specific immune effectors responsible for rejection are restricted by H-2 determinants of the recipient. Thus, haptens can be used in vivo as surrogate transplantation antigens for the study of immunopathogenic mechanisms in transplantation immunity.

Cutaneous hypersensitivity reactions to cellular isoantigens in rats.

Rats have been shown to be capable of displaying the various kinds of delayed cutaneous hypersensitivity reactions attributable to transplantation immunity previously described in guinea pigs, hamsters, rabbits, dogs, and man. The rat is unlike most other species in that much larger numbers of lymphoid cells are needed to incite these cutaneous reactions. With direct, transfer, or normal lymphocyte transfer reactions, the cutaneous responses were greater when donor and recipient differed at the Ag-B histocompatibility locus than when donor and recipient shared the same Ag-B alleles. An experiment was performed in which adult rats of a genetically defined backcross population, resulting from matings between DA and (DA x Lewis) F(1) hybrid rats, were inoculated intradermally with lymph node cells from DA rats sensitized against tissues from Lewis-strain donors. Some of the R(2) animals gave a biphasic transfer reaction with peak reactivities occurring first at 48 hr and recurring at 96-120 hr, while the others lacked this second component. Hemagglutination tests revealed that the R(2) rats giving the biphasic response possessed the Ag-B,1 antigen, which is also present in Lewis rats, whereas rats which gave monophasic reactions were homozygous for the Ag-B,4 antigenic determinant which is present in the DA strain. This suggested that the recall flare at 96-120 hr reflects proliferative activity on the part of the inoculated cells confronted by the disparate Ag-B isoantigen in the host's dermis. Skin homografts from R(1) animals bearing the Ag-B,1 antigen were uniformly rejected by DA hosts in 11 days or less, while grafts from backcross animals homozygous for the Ag-B,4 antigen usually lived longer, being rejected in 9 to 27 days. Evidence is also presented which suggests that specific isoantibodies may act synergistically with immune lymphocytes to bring about cutaneous inflammatory reactions in the rat.

Induction of anterior chamber-associated immune deviation requires an intact, functional spleen.

Anterior chamber-associated immune deviation (ACAID) expresses itself in BALB/c mice inoculated intracamerally with P815 cells in three ways: progressive growth of the tumor within the eye, transient growth of P815 cells injected subcutaneously, and prolonged acceptance of DBA/2 skin allografts. The spleen was found to play a crucial role in the development of ACAID. Splenectomized animals bearing intracameral P815 tumors reject DBA/2 skin grafts in an accelerated manner. A functioning spleen was required during the first 10 d after intracameral inoculation of P815 cells, but not thereafter. Reconstitution experiments revealed that the spleen's ability to support the induction of ACAID depends partly upon its constituent lymphoid cells, but also upon either a stromal component or a unique architectural arrangement that can only be restored with splenic fragments. The data hold promise that therapeutic protocols using appropriately timed splenectomy and specific immunization can be devised to induce hosts bearing intraocular tumors to mount an immune response sufficiently vigorous to destroy the tumor within the eye, and sufficiently precise to preserve the functional and anatomic integrity of the eye.

An analysis of graft-versus-host disease in Syrian hamsters. I. The epidermolytic syndrome: description and studies on its procurement.

F(1) hybrid hamsters derived from genetically disparate strains develop a severe and often lethal cutaneous disorder when inoculated intracutaneously with immunologically competent lymphoid cells from either parental strain, The disease is characterized clinically by extensive epidermal necrolysis, and histologically by a complete dissolution of the dermal-epidermal junction. The requisites for elicitation of this syndrome were determined to be: (a) the parental strains must differ from each other at a major histocompatibility locus, and (b) the donor inoculum must contain immunologically competent parental strain cells. In addition it was found that specifically sensitized cells surpassed normal unsensitized ones in their ability to elicit the disease, and that the disease can be transferred adoptively from affected to normal F(1) hosts by means of lymphoid cells. On the basis of these observations, it was concluded that the disease was immunologic in nature, and graft-versus-host in type. However, a series of critical studies failed to demonstrate that the epidermolysis had an immunogenetically specific basis, thus invalidating the provisional assumption that this lesion resulted from a direct immunologic attack upon parenchymal cells of the epidermis and dermis. With the aid of radiation chimeras, it was clearly established that typical epidermolysis could be induced in skin of the same genetic constitution as the attacking donor lymphoid cells. This paradox was taken into account by the possibility that, amid the intense local cutaneous graft-versus-host reactions, "skin-specific" antigenic determinants are bared which incite a quasi autoimmune response that in turn is responsible for the epidermolytic lesions.

An analysis of graft-versus-host disease in Syrian hamsters. II. The epidermolytic syndrome: studies on its pathogenesis.

The epidermolytic syndrome that can be obtained at will in F(1) hybrid hamsters by the cutaneous inoculation of adequate doses of parental strain lymphoid cells has been investigated to determine whether the cutaneous lesions are due to an autoimmune process arising from the severe, initial GVH reactions in the skin. It was amply demonstrated that inoculation of donor cells into the skin was of crucial importance to the development of epidermolysis. Parental strain lymphoid cells in similar doses delivered by any other route into normal F(1) hybrids failed absolutely to incite the acute syndrome. If "immune lymphocyte transfer" reactions incited by donor cells in the host's skin were surgically removed at timed intervals after inoculation, only complete excision within 24 hr prevented the appearance of epidermolysis in F(1) hybrid hosts, indicating that inoculated donor cells must remain within the confines of the skin for approximately 24 hr in order to evoke the disease, persistence for longer periods of time being unnecessary for the subsequent course of the disease. However, reconstitution experiments involving the intramuscular inoculation of suspensions containing mixtures of donor cells and host lymphoid cells, in the presence or absence of epidermal cells, unequivocally indicated that no intimate exposure of lymphoid cells to putative skin-specific antigens was essential. Similarly, the elicitation of generalized epidermolysis in F(1) hybrids irradiated with 300 r and then inoculated intravenously with donor cells casts further doubt on the pathogenic importance of the skin as a source of tissue-specific antigen. The results of subsequent experiments indicated that host leukocytes, rather than parenchymal cells of the dermis or the epidermis, were important contributors of the transplantation antigenic stimulus. Moreover, a series of experiments, using (CB x MHA)F(1) hybrid hosts that had been lethally irradiated and reconstituted with bone marrow cells from ALS-treated MHA donors, indicated that from 6 to 10 wk after reconstitution-when direct and immune lymphocyte transfer reactions showed a virtual absence of native F(1) leukocytes from the circulation-donor cells obtained from specifically sensitized MHA donors were completely ineffective in inducing epidermolysis, while equivalent lymphoid cell inocula derived from CB donors evoked the cutaneous disease irrespective of the time elapsed since reconstitution. To explain these findings it is postulated that in hamsters, the primary targets in graft-versus-host disease incited by the intracutaneous inoculation of donor cells are leukocytes originating in bone marrow or lymph node, or both.

An analysis of the genetic requirements for delayed cutaneous hypersensitivity reactions to transplantation antigens in mice.

The experiments reported herein provide ample evidence that mice, like most other mammalian species, are capable of displaying readily observable and reproducible delayed cutaneous hypersensitivity reactions indicative of transplantation immunity. By employing a variety of genetically defined strains, it has been shown that a genetic requirement for the development of a positive normal lymphocyte transfer reaction in mice is a difference between host and cell donor at the H-2 locus. By contrast, the immune lymphocyte transfer reaction consistently reflected the full range of histoincompatibility, both inclusive and exclusive of the H-2. It was incidentally discovered that erythema regularly accompanied delayed cutaneous reactions in the skins of female mice, whereas no local redness accompanied their counterparts in male skins. The influence of cutaneous erythema on the scoring of delayed skin reactions is discussed.

Systemic immune unresponsiveness induced in adult mice by anterior chamber presentation of minor histocompatibility antigens.

The ability to introduce carefully controlled numbers of viable cells into the anterior chamber of mouse eyes made it possible to examine the interrelationship between presentation of antigens into the anteior chamber and into conventional body sites and their synergistic/antagonistic effects on the immune system. P815 mastocytoma (DBA/2; H-2d) cells are syngeneic with BALB/c hosts at the major histocompatibility locus, but differ at multiple minor histocompatibility loci. When P815 cells were injected subcutaneously, they were rejected by BALB/c recipients who became specifically immune. By contrast, when P815 cells were injected intracamerally, they grew progressively into massive intraocular tumors; moreover, these BALB/c hosts proved subsequently unable to reject subcutaneously injected P815 cells, and, more impressively, failed to reject DBA/2 skin allografts placed orthotopically. Minor histocompatibility antigens, presented first through the anterior chamber of mouse eyes, elicit a suppressive rather than an aggressive host immune response that protects cells that bear these antigens from a destructive alloimmune reaction at both intracameral and systemic sites.

Depletion of epidermal langerhans cells and Ia immunogenicity from tape-stripped mouse skin.

To explore the relationships among Ia antigen expression, epidermal Langerhans cells, and the immunogenicity of skin allografts, cellophane tape-stripping was used in H-2 congenic and recombinant mice of defined immunogenetic disparity. Tape-stripping of murine abdominal wall skin achieved almost complete depletion of epidermal Langerhans cells within a few hours of application, as measured by cell surface ATPase and expression of Ia antigens. Tape-stripping also reduced, to a considerable degree (but not absolutely), the Ia immunogenicity of skin allografts prepared from stripped surfaces. No comparable reduction in immunogenicity of class I major histocompatibility determinants was observed, suggesting that Langerhans cells are relatively unimportant in the presentation of H-2K antigens in skin grafts. Langerhans cells reappear within 24 h of tape-stripping to anatomically intact skin, but are detectable in orthotopically grafted only after the graft has been in residence for 4 d, i.e., shortly after it has acquired a blood supply. Repopulating Langerhans cells at that time and thereafter are exclusively of host origin. These results indicate that the traffic of Langerhans cells to the skin can be extremely dynamic, especially when the epidermal surface has been markedly disturbed, and the data imply that, under normal circumstances, large numbers of Langerhans cells can be mobilized readily from an available pool of precursors.

Analysis of the mechanism of unresponsiveness produced by haptens painted on skin exposed to low dose ultraviolet radiation.

Acute, low dose ultraviolet B radiation of murine body wall skin followed by local application of DNFB produces a state of antigen-specific unresponsiveness. This state is maintained at least in part by an Lyt-1+ T cell that effects unresponsiveness by impairing the induction phase of contact hypersensitivity. The absence of suppressor cells capable of acting at the effector stage of immunity suggests that tolerogenic signals derived from the skin establish suppressor networks that are incomplete and perhaps different from networks that are induced by systemic administration of tolerogens. It is proposed that ultraviolet radiation produces its effects by impairing the antigen-presenting potential of resident Langerhans cells in whose absence hapten-derivatized keratinocytes (or their products) are able to deliver a tolerogenic signal.

The lymphoreticular system in triggering virus plus self-specific cytotoxic T cells: evidence for T help.

The thymus determines the spectrum of the receptor specificities of differentiating T cells for self-H-2; however, the phenotypic expression of T cell's specificity for self plus virus is determined predominantly by the H-2 type of the antigen presenting cells of the peripheral lymphoreticular system. Furthermore, virus specific helper T cells are essential for the generation of virus-specific cytotoxic T cells. For cooperation between mature T cells and other lymphocytes to be functional in chimeras, thymic epithelial cells and lymphohemopoietic stem cells must share the I region; killer T-cell generation also requires in addition compatibility for at least one K or D region. These conclusions derive from the following experiments: A leads to (A X B)F1 chimeric lymphocytes do produce virus-specific cytotoxic T-cell activity for infected A but not for infected B cells; when sensitized in an acutely irradiated and infected recipient (A X B)F1 these chimeric lymphocytes respond to both infected A and B. Therefore the predominantly immunogenically infected cells of chimeras the radiosensitive and by donor stem cells replaced lymphoreticular cells. In this adoptive priming model (KAIA/DB leads to KAIA/DC) chimeric lymphocytes could be sensitized in irradiated and infected F1 against KA and DC but not against infected DB targets. In contrast KBIB/DA leads to KCIC/DA chimeras' lymphocytes could not be sensitized at all in appropriately irradiated and infected F1 recipients. Thus these latter chimeras probably lack functional I-specific T helper cells that are essential for the generation of T killer cells against infected D compatible targets. If T cells learn in the thymus to recognize H-21 or K, D markers that are not at least partially carried themselves in other cells of the lymphoreticular system immunological interactions will be impossible and this paradox situation results in phenotypic immune incompetence in vivo.

Immune privilege as the result of local tissue barriers and immunosuppressive microenvironments.

As the cellular and molecular bases of immune privilege are elucidated experimentally, the phenomenon emerges as an active and dynamic exercise in immune regulation. Local tissue factors play a key role in the establishment and maintenance of privilege, particularly tissue cytokines and mediators within the local microenvironment, which modify both the induction and expression of immunity to antigens that are introduced into, or arise within, privileged sites.

Autoimmunity in the eye and its regulation.

Recent studies have provided new information concerning the development of autoimmune-mediated intraocular inflammation (uveitis) and the mechanisms that suppress this sight-robbing process. Newly collected data have led to several interesting advances: the discovery of additional uveitogenic antigens and novel uveitogenic reactions; dissection of the early steps of the pathogenic process; identification of the subsets of lymphocytes that selectively accumulate in the inflamed eye; analysis of the development of tolerance against sequestered antigens in the eye; elucidation of the cellular and molecular events of the anterior chamber-associated immune deviation, the major immunoregulatory mechanism in the eye; the capacity of this mechanism to inhibit and even treat uveitis; and examination of the mechanisms whereby oral tolerance inhibits ocular inflammation.

Promotion of syngeneic intraocular tumor growth in mice by anterior chamber-associated immune deviation.

Regressor tumors (P91 and UV-5C25), known to express potent tumor-specific transplantation antigens, were briskly rejected when transplanted either sc or ip into syngeneic mice (DBA/2 and BALB/c, respectively). These tumors demonstrated markedly different behavior following transplantation into the anterior chamber of syngeneic mice. Tumors grew to significant masses and survived for prolonged periods within the anterior chamber of the eye. The extended growth and survival of regressor tumors in the anterior chamber (i.e. immune privilege) were abrogated by splenectomy and thus resemble anterior chamber-associated immune deviation. However, this immune privilege proved to be temporary and was superseded by complete tumor resolution. Studies of mice immunosuppressed with UV light or X-ray irradiation demonstrated that spontaneous intraocular resolution of regressor tumors was due to specific systemic immunity that not only led to intraocular tumor resolution but also prevented the spread of the primary intraocular tumor to distant organs and rendered the hosts highly resistant to secondary challenge with sc tumor inocula. The present findings were relevant to understanding human retinoblastoma, an intraocular neoplasm demonstrating a high incidence of spontaneous resolution, and will hopefully form a foundation for designing, immunotherapeutic strategies for treating human intraocular neoplasms.

Infiltration and accumulation of precursor cytotoxic T-cells increase with time in progressively growing ocular tumors.

Precursors of cytotoxic T-cells (pTc) infiltrate P815 tumors growing progressively within the immunologically privileged anterior chamber (AC) of BALB/c mouse eyes, but directly cytotoxic T-cells cannot be detected in these eyes. To determine if the failure to reject these tumors is due to a relative inability of tumor-specific pTc to gain access to, or be retained by, the tumor-containing eye, we have assayed through time the frequency of pTc in eyes that received P511 tumor cells in the AC or subconjunctival space (SC; a site where the tumors are rejected). P511 tumor cells, a hypoxanthine-amethopterin-thymine medium-sensitive derivative of P815 cells, were selected for these studies because P511 tumor cells can be eliminated from in vitro lymphocyte cultures containing hypoxanthine-amethopterin-thymine medium, permitting us to make accurate estimates of pTc frequencies. To ensure that P511 cells are similar biologically and immunologically to P815 tumor cells, we demonstrated that both P511 and P815 cells form progressively growing tumors when injected into the AC of BALB/c eyes and that recipients of both tumor cell lines develop DBA/2-specific anterior chamber-associated immune deviation. Using cell suspensions harvested from eyes of mice bearing AC or SC P511 tumors, we found that tumor-specific pTc appeared first (day 8) in SC tumor-bearing eyes, compared to their appearance in AC tumor-bearing eyes (day 11). Thereafter, however, the number of pTc detected was significantly greater in eyes bearing progressively growing AC tumors than in SC tumor-injected eyes. The number and frequency of pTc we found in these eyes appeared to correlate directly with the size of the ocular tumor burden. We conclude that failure to reject P511 tumor from the AC can be ascribed neither to a quantitative deficiency in infiltrating tumor-specific pTc nor to an inability to retain pTc at the site. Our findings suggest that immune acceptance of allogeneic ocular tumor grafts may result from failure of infiltrating pTc to differentiate terminally in situ into cytotoxic effector cells.

Tumor necrosis factor alpha polymorphism correlates with deleterious effects of ultraviolet B light on cutaneous immunity.

Intradermally injected tumor necrosis factor alpha (TNF-alpha) mimics the effects of UV B light (UVB) radiation and neutralizing anti-TNF-alpha antibodies abolish the deleterious effects of UVB on induction of contact hypersensitivity suggesting that TNF-alpha is the major mediator of UVB effects on cutaneous immunity. In the present study we have shown that in lipopolysaccharide-sensitive inbred strains of mice, the ability of acute, low-dose UVB radiation to impair the induction of contact hypersensitivity to dinitrofluorobenzene is genetically determined by polymorphic alleles at the Tnf alpha locus. We have analyzed by the sequence analysis and restriction fragment length polymorphism the Tnf alpha alleles of numerous inbred strains expressing UVB susceptibility (UVB-S) and UVB-resistance (UVB-R). The Tnf alpha alleles of all UVB-R, but not UVB-S, strains contain a BamHI site in the first intron. Moreover, the 5' regulatory region of the Tnf alpha allele of UVB-R mice possesses a (CA)14 minirepeat that is located immediately 5' of the cytokine response element nearest the tumor-associated transplantation antigen box. By contrast, the Tnf alpha alleles of UVB-S mice display repeats of < > 14 at this site. It is proposed that the unique microsatellite of UVB-R mice impairs transcriptional efficiency at Tnf alpha compared to UVB-S mice and that the quantitative difference in Tnf alpha produced intracutaneously in response to UVB radiation accounts for the phenotypic traits of UVB-R and UVB-S.

Immunoregulatory mechanisms of the eye.

Immunity to protect the eye from invading pathogens is an absolute requirement for the preservation of vision. However, immune responses carry their own threat of tissue damage, due chiefly to the participation of non-specific inflammation. Because of its delicate microanatomy, the visual axis is vulnerable to distortion (and resulting blindness) from relatively trivial amounts of intraocular inflammation. Therefore, regulation of expression of immunity in the eye is critical to preservation of vision. Regulation of ocular immunity is one expression of the general phenomenon of regional immunity in which local tissue factors mold immune responses to local purposes. Ocular immune privilege is an extreme example of regional immunity. Immune privilege is an active, rather than a passive, process in which regulatory molecules and cells of the eye modulate both the induction and the expression of immunity to eye-derived antigens. Immune privilege is achieved primarily through unique features of the eye, ranging from special microanatomic factors (blood:eye barrier, absence of lymphatic draining), to soluble factors secreted by ocular cells into the ocular microenvironment, to regulatory molecules constitutively expressed on the surfaces of ocular cells. In general, the most important consequence of regulation of ocular immune responses is the virtual elimination of immunogenic inflammation from the eye. While this enables the eye to receive immune protection without the threat of blinding inflammation, it also renders the eye vulnerable to those pathogens whose elimination requires the participation of inflammatory molecules and cells.

Does innate immune privilege exist?

Immune privilege in the eye is believed to originate from the eye's need to avoid the sight-destroying consequences of inflammation. Over the past 25 years, many of the anatomical, cellular, and molecular mechanisms by which the eye avoids inflammation secondary to adaptive immune responses have been elucidated. In the recent past, it has become increasingly clear that innate immune responses play a critical role in activating the adaptive immune response. Moreover, innate immunity itself carries a heavy burden of inflammation, thereby posing a threat to vision if it should occur intraocularly. Ocular immunologists have now begun to inquire into the extent to which the eye regulates the expression of innate immunity in oculi. Evidence is presented which indicates that factors found in normal aqueous humor (1) prevent NK cells from lysing their targets, (2) inhibit neutrophil activation by CD95 ligand, (3) suppress nitric oxide production by activated macrophages, and (4) interfere with complement activation via the alternative pathway. These factors include transforming growth factor-beta2, alpha-melanocyte-stimulating hormone, calcitonin gene-related peptide, and migration inhibitory factor. The ability of the eye to prevent intraocular activation of innate immune effectors spares the corneal endothelium (which expresses CD95 ligand constitutively, but low levels of MHC class I molecules) from destruction by NK cells and neutrophils, and protects the visual axis from distortion by macrophage and complement-mediated inflammation. Thus, privilege exists in the eye for both adaptive and innate immunity.