H-2 restriction for lymphocyte homing into lymph nodes

The early days of NK cells: an example of how a phenomenon led to detection of a novel immune receptor system - lessons from a rat model

In this review, I summarize some of the early research on NK cell biology and function that led to the discovery of a totally new receptor system for polymorphic MHC class I molecules. That NK cells both could recognize and kill tumor cells but also normal hematopoietic cells through expression of MHC class I molecules found a unifying explanation in the “missing self” hypothesis. This initiated a whole new area of leukocyte receptor research. The common underlying mechanism was that NK cells expressed receptors that were inhibited by recognition of unmodified “self” MHC-I molecules. This could explain both the killing of tumor cells with poor expression of MHC-I molecules and hybrid resistance, i.e., that F1 hybrid mice sometimes could reject parental bone marrow cells. However, a contrasting phenomenon termed allogeneic lymphocyte cytotoxicity in rats gave strong evidence that some of these receptors were activated rather than inhibited by recognition of polymorphic MHC-I. This was soon followed by molecular identification of both inhibitory and stimulatory Ly49 receptors in mice and rats and killer cell immunoglobulin-like receptors in humans that could be either inhibited or activated when recognizing their cognate MHC-I ligand. Since most of these receptors now have been molecularly characterized, their ligands and the intracellular pathways leading to activation or inhibition identified, we still lack a more complete understanding of how the repertoire of activating and inhibitory receptors is formed and how interactions between these receptors for MHC-I molecules on a single NK cell are integrated to generate a productive immune response. Although several NK receptor systems have been characterized that recognize MHC-I or MHC-like molecules, I here concentrate on the repertoires of NK receptors encoded by the natural killer cell gene complex and designed to recognize polymorphic MHC-I molecules in rodents, i.e., Ly49 (KLRA) receptors.

Immune response: tissue specific T-lymphocytes

The lymphatic system forms a 'blind' plexus of vessels that in general are found in tissue which has an inherently high replicative capacity. It is this system that is responsible for the rapid deployment and circulation of tissue-specific T-lymphocytes for the inspection of cell-surface aberrations within the tissue. The presence of tissue-specific T-lymphocytes explains why 90% of lymphocytes are found outside the lymphatic system and why they migrate in a selective manner. The tissue-specific T-lymphocyte is considered to express a common lymphocyte cell surface pattern, the homotype, and a tissue-specific cell-surface pattern, the histotype which may involve MHCA and mHCA. It is the histotypic pattern that is responsible for the tissue specificity of the tissue-specific T-lymphocyte. The presence of tissue-specific T-lymphocytes does pose problems for the immune system. If different tissue-specific T-lymphocytes met within a particular tissue, 'lost' lymphocytes, an immune response will be generated against the intruder (lost lymphocyte), and the intruder will not be able to recruit other immunocompetent cells in that tissue. This immune reaction is an attempt to change the histotypic pattern of the intruder. This situation would explain the autologous immune response. This response however is suppressed in the systemic system by immunosuppressive compounds from the liver. It is only in the tissues that the tissue-specific T-lymphocytes are released from this suppression, in order to initiate immune reactions against aberrant cell-surface patterns.

Anti-Ia monoclonal antibody (10-2.16) inhibits lymphocyte-high endothelial venule (HEV) interaction

Lymphocyte egress from the vascular compartment into the lymph node (LN) parenchyma occurs at the postcapillary venules, termed high endothelial venules (HEVs). Lymphocyte adhesion and migration through the HEVs is a receptor-mediated, energy-dependent, process. The aim of this study was to investigate the role of MHC Class II antigen expression on lymphocyte-HEV interaction in normal (CBA) and autoimmune (MRL/l) mice. Using the HEV binding assay, lymphocyte adhesion to LN sections pretreated with monoclonal antibody (MAb; 10-2.16) was decreased compared to diluent (mean of the differences +/- standard deviation; xd +/- SD: 0.749 +/- 0.22, P less than 0.0075)- and myeloma immunoglobulin-pretreated controls (xd = 0.462 +/- 0.13, P less than 0.005). Similar inhibition of binding was found in MRL/l LN sections pretreated with MAb 10-2.16. Binding inhibition was concentration dependent, but total inhibition was never achieved. Several other anti-Ia MAb's were used, but failed to inhibit lymphocyte attachment. Lymphocyte binding to control sections treated with MAb's against MHC Class I antigen, plasminogen activator (PAM-3), anti-thrombin III (AT-IIIm), and MECA-325 antigen was not significantly different from diluent controls. LN cell suspensions pretreated with MAb 10-2.16 bound normally to LN sections. By contrast, MAb to lymphocyte homing receptor (MEL-14) inhibited lymphocyte adhesion. The role of Class II antigens in lymphocyte-HEV interactions is discussed.

Inhibition of HLA class I antigen and mRNA expression induced by Rous sarcoma virus in transformed human fibroblasts

Cells from various human nonlymphoreticular neoplasms show reduced HLA class I antigen expression. In this report, a system of human fibroblasts transformed by an avian retrovirus has been employed to investigate the mechanism of this phenomenon. Rous sarcoma virus has been used to transform in vitro human dermal fibroblasts, and clonal cell lines have been established from these cultures. In all the clones studied the integration of the provirus induced a reduction of cell-surface HLA-A, -B, -C framework antigen and beta 2-microglobulin expression when compared to levels for the respective parental fibroblasts. The reduction was correlated with a diminished intracellular synthesis of these molecules. Uninfected cells derived from an osteogenic sarcoma exhibited a reduced expression comparable to that of dermal diploid fibroblasts obtained from the same donor and transformed by Rous sarcoma virus. RNA gel blot analysis of total cellular RNA and of poly(A)+ cytoplasmic RNA showed a markedly decreased amount of HLA class I transcripts in the transformed cells. Southern blot study of genomic DNAs digested with several restriction endonucleases showed that the banding patterns of the HLA genes were not altered in the cells harboring the Rous sarcoma provirus. Our data are consistent with the hypothesis that the Rous sarcoma provirus that does not seem to be linked to the major histocompatibility complex class I gene superfamily may negatively control HLA gene expression.

Analysis of the genetic control of lymphocyte positioning

A possible role for the major histocompatibility complex (MHC) in the localization of lymphocytes in different lymphoid organs was investigated using inbred mouse strains. Lymphocytes labelled with the intracellular fluorochrome Hoechst 33342 (H33342) were transfused intravenously (IV) into unimmunized mice and the distribution of these labelled lymphocytes examined. In some combinations (e.g. C57BL/6----CBA) 2 h after injection allogeneic lymphocytes accumulated in the region between the marginal zones and outer aspects of the white pulp of the spleen. In contrast, in syngeneic controls (e.g. CBA----CBA) the lymphocytes migrated normally into the while pulp. Similar results were obtained in Peyer's patches. Mapping studies in the spleen indicated that the failure to migrate normally is predominantly controlled by the MHC complex, although some non-MHC genes may play a role. In the case of the MHC the most definitive combination was BALB/c-H-2dm2 (H-2L deletion mutant) lymphocytes transfused into BALB/c recipients, the mutant lymphocytes failing to migrate normally and, therefore, implicating the H-2L region in the phenomenon. No differences in the viability of labelled lymphocytes at 6 and 24 h after injection into either syngeneic or allogeneic recipients suggests that the inability of cells to passage through lymphoid organs may represent inappropriate receptors rather than elimination of the allogeneic lymphocytes by natural killer cells (NK) as previously proposed.

Neonatal tolerance induction in the thymus to MHC-class II-associated antigens. I. Preferential induction of tolerance to Mls antigens and resistance to allo-MHC antigens

Neonatal tolerance inducibility of self-major histocompatibility complex (MHC)-class II-associated antigens was compared with that of allo-class II antigens. BALB/c (H-2d, Mlsb) mice, less than 24 hr after birth, were intravenously injected with bone marrow cells of either (BALB/c X DBA/2)F1 (H-2d, Mlsb/a, semiallogeneic at the Mls locus) or (BALB/c X B10.BR)F1 (H-2d/k, Mlsb; semiallogeneic at the MHC), as antigens. The mice were tested for in vivo immune activity of class II-reactive T cells by means of the popliteal lymph node-swelling assay. They developed tolerance, irrespective of type of antigens, showing profoundly suppressed host-versus-graft reaction, and those tolerized to the allo-MHC antigens accepted skin grafts of the corresponding allogeneic mice. In the thymus and spleen of the Mls-tolerant mice, antigen-specific class II-reactive T-cell activity was completely abolished, without the apparent involvement of suppressor cells. In contrast, the activity in allo-MHC-tolerant mice was not reduced in either thymus or peripheral lymphoid organs, suggesting that systemic hyporesponsiveness is attributable to reversible suppression of immune competent cells. The resistance for cell-level tolerance induction to allo-class II antigens may not be ascribed to the active participation of allo-MHC antigens in prevention of or in escape from tolerance induction or both, since an injection of bone marrow cells of both Mls and H-2-semiallogeneic (DBA/2 X B10.BR)F1 (H-2d/k, Mlsa/b) mice could induce tolerance to Mlsa-H-2d antigens in newborn thymus cells.

Studies on lymphocyte homing in autoimmune prone NZB mice

Lymphocyte homing patterns in young (3-5 months old) and old (10-12 months old) autoimmune prone NZB mice were investigated by transferring 51Cr labelled lymphoid cells into syngeneic and H-2 compatible allogeneic recipients. We confirmed that non H-2 alloantigens as well as H-2 alloantigens can be important determinants of apparent abnormalities of cellular distribution with the techniques employed. No gross abnormalities of lymphocyte traffic were present in the young NZB mice as compared to the autoimmune resistant strains of mice when syngeneic cells are used. Spleen of older NZB mice appeared to be less attractive to lymph node cells than was the spleen from young NZB mice. Splenocytes of older NZB mice localized significantly more in the liver and less in the lymph nodes as compared with splenocytes from young NZB mice. The mechanism underlying abnormalities of lymphoid cell distribution which feature the autoimmune-prone NZB mice are not yet clear and further studies will be necessary before they can be characterized definitively. Our findings, using syngeneic cells, are in disagreement with those of Zatz and Lance since evidence of abnormal distribution of lymphocytes in young NZB mice were not seen when syngeneic cells were employed.

Nonmetastatic tumor cells acquire metastatic properties following somatic hybridization with normal cells

Somatic cell hybridization between nonmetastatic tumor cells and normal cells of the lymphoreticular system results in hybrid cells manifesting metastatic properties of defined target organ specificity. Thus, fusion of the nonmetastatic BALB/c originated NSI plasmacytoma with C57BL B lymphocytes resulted in hybridomas, each of which were metastatic. Of 10 hybridomas, 7 generated metastases in the spleen and liver, whereas 3 generated liver metastases. The generation of liver metastases by hybridomas which homed to both spleen and liver, but not by those which homed to the liver only, was controlled by the spleen. The acquisition of metastatic properties via somatic cell fusion seems to represent a general principle, in which the normal partner determines the target organ specificity for the metastatic growth. Thus, fusion of SP2/O myeloma cells with syngeneic B lymphocytes also resulted in a hybrid cell metastasizing to the spleen and liver, yet a somatic hybrid between NSI and a macrophage or dendritic-like cell metastasized to the lung. Cell surface molecules encoded by the genome of the normal partner was demonstrated to control the target organ specificity: antibodies against MHC-encoded antigens of the normal B cell partner prevented the generation of metastases by hybridomas metastasizing to the spleen and liver, but not by those metastasizing to the liver only. This is in accordance with the function of MHC molecules on lymphocytes in controlling their homing to lymphoid organs. Hybridomas of T cell lymphomas also manifested metastatic properties. Analysis of the cell surface Thy-1 antigens of a hybridoma (DCH10), produced via somatic fusion between BW5145 lymphoma and a putative macrophage cell indicated that cells of liver metastases (DCH10-Li) generated by the hybrid cells might have undergone further somatic cell fusion in vivo with host (T?) cells. These cells have acquired new metastatic properties, generating metastases in spleen, liver and kidneys. In fact, even the inoculation of the parental BW lymphoma cells resulted in a case of liver metastasis (BW-Li). Such BW-Li cells, upon reinoculation, also generated metastases in the spleen, liver and kidneys. Analysis of the Thyl phenotype indicated that BW-Li cells may also have undergone somatic cell fusion in vivo with host (T?) cells, resulting in the acquisition of metastatic properties. The pattern of cell-cell interactions (adhesion, infiltration) with liver cell monolayers of BW-Li cells and of DCH10-Li (T-cell lymphomas) was identical, and differed from cells of liver metastases of the myeloma-B cell hybridomas which might be based on responses to liver growth signals.(ABSTRACT TRUNCATED AT 400 WORDS)

A genetic analysis of natural resistance to nonsyngeneic cells: the role of H-2

The genetic control of natural resistance in vivo to four natural killer (NK) cell-resistant H-2 homozygous lymphoid tumor cell lines was investigated by following the survival and organ distribution of cells prelabeled with radioactive iododeoxyuridine. Backcross mice derived from DBA/2J and CBA/J parents were injected with H-2d tumor cells and tumor cell elimination was lowest in H-2d homozygotes. Natural killer cell activity was also reduced in mice with the H-2d haplotype, but no direct correlation between NK cell levels against YAC-1 or SL2-5 lymphoma cells and natural resistance in vivo was demonstrable. Analysis of 23 BXD recombinant inbred strains indicated that natural resistance to H-2d tumors was restricted to H-2b strains. There was no direct association of NK cell activity with H-2 type in the BXD strains and NK cell levels did not correlate with tumor survival in vivo. By comparing natural resistance to H-2d and H-2b tumors in DBA/2, C57BL/6, B6D2F1, and B10.D2 mice we found that H-2 nonidentity between the tumor and the host, rather than the host H-2 haplotype, determined whether natural resistance occurred. Again, NK cell activity against YAC-1 cells was not predictive of tumor survival in these strains. These results provide genetic evidence that NK cells alone cannot account for natural resistance to H-2 nonidentical cells of hemopoietic origin.

The rapid elimination of allogeneic lymphocytes: relationship to established mechanisms of immunity and to lymphocyte traffic

Allogeneic lymphocyte cytotoxicity (ALC) refers to the destruction of lymphocyte beginning within a few hours of intravenous injection into non-sensitized, allogeneic recipients. Usually this has been detected in rats and mice by comparing the localization of 51Cr-labelled lymphocytes in the tissues of allogeneic and syngeneic recipients. In a particular strain combination the existence of ALC is supported by deficient localization of allogeneic lymphocytes in the LN, lungs and blood mononuclear population and an excess of the label that had been associated with allogeneic cells in the lymph plasma, blood plasma and kidneys. As the destruction of the allogeneic cells occurs in the lymphatic tissues, especially the spleen, it is paradoxical that there is sometimes an excess of the label associated with allogeneic cells in the spleen but evidence is presented that most of the isotope is no longer associated with living cells in that organ at 24 h after transfer. The data cannot be explained by an altered distribution of allogeneic lymphocytes between different organs. Experiments on the early migration of lymphocytes from the blood of syngeneic and allogeneic recipients point unequivocally to the conclusion that the adhesion of lymphocytes to specialized vascular endothelium in LN and their consequent entry into LN does not require that the lymphocytes and the endothelial cells share MHC products. The characteristics of ALC stressed in this review include the following: 1) it is independent of T-cell activation, either of host T-cells or of donor T-cells: 2) B- and T-cells are about equally vulnerable to ALC; 3) it varies greatly between different strain combinations regardless of other indices of cellular and humoral immunity; 4) F1 hybrid donor cells are vulnerable but the effect is always less marked than with allogeneic cells; 5) ALC is less radio-sensitive than primary cellular or humoral immune responses; 6) adoptive transfer of ALC can be achieved with TDL from nude rats. The possible mechanism underlying ALC has been debated in terms of natural killer cells recognizing certain allo-antigens or alternatively pre-existing "natural" antibody with low affinity for allogeneic cells leading to their elimination by ADCC. The argument hinges on the necessity for antibody and cannot be resolved by current data.

Lymphocyte migration across major histocompatibility barriers in splenectomized rats

Localisation and migration patterns of iv injected radio-labelled thoracic duct (TD) lymphocytes were studied in particular with regard to passage through lymph nodes and re-entry into thoracic duct lymph. To avoid unwanted splenic sequestration of migrating lymphocytes presenting alloantigens to the recipient, only splenectomized recipients were used. Donor cells and recipients differed at the MHC (RT-1) locus, either in fully allogeneic (AO -- greater than BN and v.v.) or semi-allogeneic (AO -- greater than AO X BN and v.v.) combinations. In two of these combinations (BN -- greater than AO and AO X BN -- greater than AO) deficient output in TD lymph correlated with deficient localisation in lymph nodes and high amounts of radioactivity in the liver. In the other allogeneic combination (AO -- greater than BN), however, high TD output (i.e. when compared with the syngeneic combination BN -- greater than BN) correlated with good localisation in lymph nodes and low (control) levels of radioactivity in the liver. It was postulated that lymphocyte migration from blood to lymph under these circumstances can only be studied as an artifact secondary to whether or not migrating cells are removed from the circulation before they can reach and cross HEV's. These Allogeneic (or Altered) Lymphocytes Removing Tissues (by definition: Extranodular) may (conceptually) be comprised within one system: ALERT. It is our working hypothesis that the study of lymphocyte migration across (major) histocompatibility barriers is seriously impaired by the functioning of ALERT. It might be worthwhile to try and create conditions in which interference by this system is prevented, e.g. by using tolerant animals or bone-marrow chimeras.

Involvement of interferon in virus-induced lymphopenia

Intraperitoneal injection of vesicular stomatitis virus (VSV) into mice causes marked and rapid changes in leukocyte distribution. The virus induces an increase in peripheral blood (PB) granulocytes and an extensive decrease in the lymphocyte count which reaches a nadir of less than 10% of preinfection values, 12 hr after virus inoculation. In the lymph nodes and spleen extensive lymphocyte translocation and granulocyte infiltration are observed. Most changes abate 48 hr following virus inoculation. Injection of poly(rI):(rC) causes similar changes to those observed with VSV. The lymphocyte changes observed after injection of VSV or poly(rI):(rC) coincide with high levels of interferon (IFN) in the serum. We have examined the effects of anti-IFN antibody on those changes and investigated whether they can be mimicked by injecting IFN. Our findings suggest that the IFN induced by VSV or poly(rI):(rC), rather than those agents themselves, causes the observed lymphopenia as well as some of the changes observed in the spleen. On the other hand, the effects of VSV on granulocyte localization do not appear to be mediated by IFN.

Natural cytotoxicity in rats: radiation-induced changes in the early killing of allogeneic cells

In some strain combinations among inbred rats intravenously injected 51Cr-labeled lymphocytes are rapidly destroyed in substantial numbers by unsensitized allogeneic hosts. This phenomenon has been referred to as natural cytotoxicity (NC) and is characterized by decreased lymph node radioactivity, increased kidney and urine radioactivity, and to a lesser extent increased liver radioactivity in allogeneic hosts, when compared with the distribution of label in syngeneic recipients of the same cell suspension. A single exposure to 800 rad either 1 or 7 days before the injection of 51Cr-labeled lymphocytes effected a reduction in NC as defined by all the above parameters in a strain combination exhibiting high NC. The same dosage of radiation abolished NC in a strain combination exhibiting intermediate leads to low NC. Because NC was not always completely abolished, the phenomenon was held to be partially radiosensitive. An increased accumulation of 51Cr-labeled lymphocytes was seen in the lymph nodes of both syngeneic and allogeneic irradiated hosts when compared with nonirradiated controls, although the increase was greater in allogeneic than in syngeneic hosts. This increased colonization in the lymph nodes of irradiated hosts seemed unlikely to be due to an increase in the available "space' in the lymph nodes following irradiation.

In vivo elimination of allogeneic lymphocytes in normal and T-cell-deficient rats. Elimination does not require T cells

The distribution of allogeneic and syngeneic thoracic duct lymphocytes was studied over 24 h in normal and T-cell-deficient animals (thymectomized, irradiated rats, 'B rats', or congenitally athymic nude rats). Initial migration from blood was no less for allogenic than for syngeneic cells. After 24 h, however, a marked deficit of radioactively labelled allogeneic cells as compared with syngeneic cells was found in the lymphoid tissue, whereas the allogeneic isotope was recovered in a relatively greater amount in liver, kidneys, and cell-free plasma and lymph. Most of the allogeneic cells are evidently destroyed within the first 24 h and their isotope released into body fluids. Our studies also revealed this process to be even more evident in T-cell-depleted environments. Autoradiographic studies of recipient nude rat spleens showed that allogeneic cells were not found in the great number seen in syngeneic transfers, but a high grain density in the periarteriolar lymphocyte sheath area could be observed. Granula seemed to be predominantly located over large nonlymphoid cells. The elimination of allogeneic lymphocytes is therefore governed by mechanisms independent of an intact thymus and may be due to a cell population or factor more active in nude animals than in their non-nude littermates.

Autoradiographic analysis of lymphocyte migration into the mammary epithelium and milk of lactating female rats

Adoptively transferred radiolabeled lymphoid cells migrating to the lactating mammary gland were shown to enter the alveolar epithelium and ultimately the milk. Lactating female rats were injected intravenously with [3H]uridine-labeled syngeneic mesenteric lymph node cells, and the distribution of the cells 24 and 48 h later within intestinal and mammary tissues and their presence in milk were assessed autoradiographically. At both time periods, numerous labeled cells were found in the Peyer's patches and mesenteric lymph nodes. The mammary tissue and intestinal mucosa (lamina propria and epithelium) contained fewer labeled cells per unit area than those sites. Labeled cells within the mammary tissue were distributed equally between the alveolar epithelium and the intralobular connective tissue, where they were seen in both blood vessels and in the loose connective tissue. Occasional labeled cells were observed among the mononuclear cells seen in the alveolar lumina, and an average of 4.8% of the cells harvested from milk samples were labeled. Labeled cells within the secretory epithelium and milk always had the morphologic characteristics of mononuclear leukocytes. Thus, at least a portion of the lymphoid cells which have been shown to migrate to the mammary tissue in increased numbers during lactation actually enter and traverse the epithelium and contribute to the lymphoid component of mammary secretions.

Resistance to cell-mediated cytotoxicity is correlated with reduction of H-2K gene products in AKR leukemia

AKR leukemia cell lines differing in the amount of H-2K and H-2D antigens expressed on the cell surface were used to assess cell-mediated immune responses in syngeneic mice against Gross/AKR murine leukemia virus (MuLV)-induced tumors. Leukemic cells with reduced expression of H-2Kk antigens were inactive as inducers of Gross-MuLV/H-2k-specific cytotoxic T lymphocytes (CTL) and resistant to lysis by CTL raised against H-2Kk positive AKR leukemia cells. H-2Kk positive leukemias induced cytotoxic effectors, which upon restimulation in vitro, lysed the stimulating and other H-2Kk positive leukemia cells. In antibody inhibition experiments, T-cell-mediated cytotoxicity to these leukemias could only be inhibited by antisera and monoclonal antibodies specific for the H-2Kk antigens. Due to this specific role of H-2Kk antigens in T-cell cytotoxicity to Gross/AKR MuLV-induced tumors, reduced expression of H-2Kk antigens on spontaneous AKR leukemic cells could have important implications for surveillance of these neoplastic cells.

The route of migration of lymphocytes from blood to spleen and mesenteric lymph nodes in the pig

Porcine peripheral blood lymphocytes were labelled with tritiated uridine in vitro and transfused into normal young pigs. Serial biopsies were taken from the spleen and mesenteric lymph nodes, and the localization of labelled lymphocytes determined on autoradiographs. Four to five hours after cell infusion samples of Peyer's patches, tonsils and small intestine were taken and the labelled lymphocytes classified by their localization in different organ compartments. In spleens most labelled cells were found in the red pulp and about 30% in the marginal zone. Within 4 to 5 h there was a constant increase in labelled lymphocytes in the compartment of the white pulp with more cells localized in the periarteriolar lymphatic sheath than in the corona. In lymph nodes about two thirds of all labelled cells were seen in the wall of high endothelial venules 15 min after cell infusion. Labelled cells then decreased in the vessel wall, but, at the same time, increased in the neighbourhood of these vessels and other parts of the paracortex. After 5 h about 10% of labelled lymphocytes had already migrated into the corona. In tonsils and Peyer's patches a comparable distribution of labelled cells was found in the organ compartments. The kinetics and the route of migration in the spleen and lymph nodes are therefore comparable to data for other species, despite the peculiar structure of pig lymph nodes and the paucity of lymphocytes in efferent lymphatics in pigs.

Maintenance of allogeneic cell recognition in allograft tolerant mice

The organ distribution of 51Cr-labelled lymph node cells following transfer to syngeneic, allogeneic and specifically tolerant allogeneic recipients were compared. Neonatal induction of transplantation tolerance in several donor-recipient combinations involving different H-2 haplotypes had no effect on the reduction of homing into lymph nodes and the values of the homing did not differ from those of the untreated allogeneic recipients. In both cases, they amounted to 45-55% of the syngeneic controls. Even those neonatally treated animals, which had not been rendered tolerant at birth and rejected test skin grafts, were not capable of removing the transferred allogeneic cells by a typical immune elimination. The results indicate that animals recognize allogeneic cells, irrespective of whether or not they reject test skin grafts.

H-2D antigens released by thymocytes and cell adhesion

The identity and complete purification of mouse Thymocyte Interaction Modulation Factor (T IMF) is described. Use of silver-stained PAGE methods shows that previous methods of purification yield preparations containing two protein or glycoprotein bands. T IMF activity from H-2k mice can be bound to 15.5.5 monoclonal antibody columns (anti H-2 Dk) but not to 11.4.1 columns (anti H-2 Kk). The activity can be recovered from 15.5.5 columns and runs on PAGE aa a single band at approximately 34,000 Daltons. This evidence together with previous evidence relating the activity to H-2D locus argues that T IMF is a soluble H-2 D antigen fragment equivalent to a papainized H-2 fragment. Additional evidence is presented on an improved method of assay of T IMF activity, on its inactivation by enzymes and serine-esterase inhibitors and of its effect on syngeneic leucocytes and macrophages. It is shown that T IMF is not appreciably toxic cells.

Variation of expression of histocompatibility antigens on tumor cells: absence of H-2Kk-gene products from a gross-virus-induced leukemia in BALB.K

The antigenic profile of the K-GV tumor of BALB.K origin, induced by Gross virus and maintained in vitro and in vivo, was investigated by serological and immunochemical methods and techniques of cell-mediated immunity. The H-2Kk-gene products were absent by several criteria: (1) monoclonal antibody and conventional alloantisera directed against eh H-2Kk antigenic specificities were nonreactive by direct testing and by absorptions. (2) H-2Kk products could not be precipitated from glycoprotein or protein extracts of the radiolabeled K-GV tumor. (3) Cytotoxic effectors against H-2Kk produced by sensitization in vitro and in vivo failed to kill K-GV target cells. (4) The tumor could neither stimulate BALB.B congenic mice to produce cytotoxic effectors nor specific cytotoxic antibody against H-2Kk-gene products. In contrast, the H-2Dk antigen was readily detectable by all these criteria. These findings therefore describe a tumor which has selectively lost the H-2K-gene products. The K-GV tumor was able to generate Gross-virus specific CTL, but had greatly reduced susceptibility to lysis by Gross-virus specific CTL generated by H-2K expressing AKR (H-2k) tumors. These findings have important implications for the associative recognition of tumor antigens and the immune surveillance of virally induced tumors.

Is the MHC a general self-recognition system playing a major unifying role in an organism?

From the review of several recent observations of cell-cell interactions, which occur preferentially in autologous or syngeneic situations such as rosettes, adhesion, homing, and contact inhibition, the existence of an active general process of cellular self-recognition, not limited to the immune system, is postulated. This process is MHC associated or dependent, and seems to require an identity of ubiquitous molecules of class I--or other linked gene products at the surface of interacting cells. In contrast, class II molecules are not apparently implicated in general self-recognition. The immune system is regarded as a late evolution from a self-recognition system. It retains the ability of self-evolution, but possesses the exclusive property of active discrimination against foreignness. The astonishing fact that identity of MHC products seems to be needed for recognition is discussed in the context of various possible mechanisms. From immunological and genetical consideration, it is proposed that the genuine biological role of the MHC would be that of a self-recognition and unifying system.