Positive and negative thymocyte selection induced by different concentrations of a single peptide

T lymphocyte maturation is dependent on interactions between the T cell receptor (TCR) expressed on the developing thymocyte and intrathymic major histocompatibility complex (MHC)-peptide ligands. The relation between the peptide-MHC complex that results in negative or positive selection has not been identified. Here, the requirements for the maturation of thymocytes expressing a defined transgenic TCR specific for a viral peptide are studied in fetal thymic organ culture. Low concentrations of the viral peptide antigen recognized by this transgenic TCR can mediate positive selection, whereas high concentrations result in thymocyte tolerance. These findings support the affinity-avidity model of thymocyte selection.

CD4+ class I-restricted T cells specific for HIV gp160 315-329

Mature, circulating, alpha beta T cells express either CD4 or CD8. In the majority of cases, CD4+ T cells recognize Ag in association with class II MHC molecules, while CD8+ T cells recognize Ag in association with class I MHC molecules. In this report we describe CD4+ class I-restricted T cell hybridomas and normal clones specific for the peptide 315-329 of HIV gp160 strain IIIb in association with H-2Dd. Two models were formulated to explain how CD4+ class I-restricted T cells could arise. First, they could represent aberrant selection of CD4+ cells on class I MHC molecules in the thymus. Alternatively, they could have been selected normally on class II; in this case the cells would display cross-reactive recognition of 315-329 in association with H-2Dd and an unknown Ag in association with class II. To distinguish these models, a second specificity was determined for the T cell clones. The normal clones recognized the class I molecule H-2Kk as alloantigen and thus were presumably positively selected in the thymus on class I MHC. CD4 was shown to be functional in these cells in that anti-CD4 mAb inhibited their proliferation: however, both Ag- and Con A-induced responses were inhibited, suggesting that a negative signal was delivered by the anti-CD4 mAb.

Effect of H-2 compatibility in autoimmune destruction of islet allografts from B10 congenic lines to nonobese diabetic mice

Autoimmune diabetes involves multiple antigens, and both cellular and humoral immune responses. Using CBA (H-2k) C57BL/6 (H-2b), and BALB/c (H-2d) newborn mouse pancreata, we previously demonstrated that acute and strong destruction of islet allografts by anti-islet autoimmunity in the nonobese diabetic (NOD) mouse H-2Kd, Db) is under the influence of major histocompatibility complex (MHC) antigens. In the current study, we have attempted to confirm these results in the absence of minor alloantigenic differences using B10 congenic strains as pancreatic donors. Pancreata from B10.BR (H-2k), C57BL/10SnJ (H-2b), and B10.D2 (H-2d) were transplanted under the kidney capsule of NOD mice within 1 month of diabetes onset. These recipients were immunosuppressed with cyclosporine (CsA) in a dosage that effectively prevents rejection of skin allograft, but not islet isograft destruction that is mediated by anti-islet autoimmunity. On day 10, the grafts were harvested and examined histologically to assess viability. Pancreatic allografts from B10.D2, sharing the H-2Kd with the NOD mouse, showed the strongest lymphocytic infiltration, and neither islets nor beta cells were found in all seven grafts. C57BL/10SnJ grafts, sharing the same H-2Db, also showed severe lymphocytic infiltration, and no intact islets, and only a few beta cells were found, as single cells, in three of eight grafts. In contrast, B10.BR grafts, completely incompatible at the H-2, showed the least infiltration, and normal islets containing many beta cells were found in 10 of 11 grafts. These results again suggested the hypothesis that islet allograft destruction by diabetic NOD mice is MHC restricted.(ABSTRACT TRUNCATED AT 250 WORDS)

'Lupus-prone' mice are susceptible to organ-specific autoimmune disease, experimental allergic encephalomyelitis

Immunization with the multideterminant autoantigen myelin basic protein (MBP) causes experimental allergic encephalomyelitis (EAE), a T-cell-mediated autoimmune disease that serves as a model for multiple sclerosis (MS). MBP peptides Ac1-11 and p35-47 induce potent EAE in mice of the H-2u haplotype. T cells specific for Ac1-11 predominantly utilize one T-cell receptor (TCR) V beta gene segment, V beta 8.2. All T-cell clones and hybridomas analyzed, regardless of TCR V beta usage, utilize D beta 2 and J beta 2 elements. The NZW mouse strain (H-2z), which contributes to the spontaneous 'lupus-like' illness in (NZB x NZW)F1 mice, has a genomic deletion encompassing D beta 2 and J beta 2 gene segments. The NZW strain expresses class II (I-A and I-E) genes which share identical sequences with H-2u class II. We investigated whether these strains are susceptible to EAE induced with intact MBP and known encephalitogenic MBP peptides. In vitro analysis demonstrated that NZW antigen-presenting cells (APC) can present MBP and MBP peptide Ac1-11 to an encephalitogenic T-cell clone derived from an H-2u mouse, confirming the functional identity of NZW class-II (I-A) molecules with their respective H-2u class-II gene products. In vivo results demonstrated that NZW and (NZB x NZW)F1 mice are susceptible to EAE induced with intact MBP and Ac1-11. MBP p35-47 caused EAE in (NZB x NZW)F1 mice, which express alleles for both the normal (NZB) TCR beta-gene locus, and the abnormal (NZW) TCR beta-gene locus containing the J beta 2 deletion.(ABSTRACT TRUNCATED AT 250 WORDS)

Augmentation of pathogenesis of coxsackievirus B3 infections in mice by exogenous administration of interleukin-1 and interleukin-2

Two variants of coxsackievirus B3 (CVB3) which differ dramatically in the ability to induce myocarditis in BALB/c mice were studied. H3 virus infection of murine monocytes in vitro resulted in release of concentrations of interleukin 1 (IL-1) and alpha/beta interferon that were high compared with those of cells infected with the H310A1 virus variant. In vivo, H3 virus infection caused substantial inflammatory cell infiltration of the myocardium, and lymphocytes from these animals gave predominantly Th1-cell responses to either whole H3 virus or overlapping peptides of the CVB3 vp1 capsid protein, as determined by IL-2 production. In contrast, H310A1 virus infection produced minimal myocarditis and Th1-cell responses, but Th2-cell activation was more pronounced than in H3 virus-infected mice (as determined by IL-4 concentrations). Exogenous treatment of H310A1 virus-infected mice with either IL-1 or IL-2 restored both myocarditis susceptibility and Th1-cell responses to whole virus and vp1 peptides. Furthermore, H310A1 virus-infected mice given exogenous IL-1 showed substantial in situ IL-2 deposition in the myocardium. These results indicate that CVB3-induced myocarditis may depend upon release of specific cytokines during infection and that activation of Th1 cells may be an important factor in pathogenesis.

The suppressor factor of T suppressor cells induced by tolerogenic conjugates of ovalbumin and monomethoxypolyethylene glycol is serologically and physicochemically related to the alpha beta heterodimer of the T cell receptor

Ovalbumin-specific, H-2Kd restricted, CD8+ Ts cells of clone 17.2 were shown to produce an OVA-specific Ts cell factor (TsF17.2) possessing the same Ag specificity and MHC restriction as those of the intact Ts cells. The Ts cell clone was generated from a single cell of the spleen of a mouse which had been immunosuppressed by injection of tolerogenic OVA(mPEG)12 conjugate. For the elucidation of the nature of TsF17.2, it was characterized by serologic, physicochemical, and Western blot analyses. It was found that 1) the OVA-specific suppression of in vitro antibody production by TsF17.2 could be blocked by mAb H28-710 which binds to an epitope of the constant region of the alpha-chain of TCR; 2) the TsF17.2 could be sequestered by, and eluted from, immunosorbents prepared by coupling to Affi-Gel Hz the H28-710 mAb or the mAb H57-597 and F23.1 which are specific, respectively, for an epitope of the constant region of the beta-chain and an epitope of the V beta 8 region of the TCR; and 3) the TsF17.2 had a pl of 7.0, m.w. of 84,000, and consisted of two disulfide-linked subunits of 42,000 each. After electroelution from the SDS-PAGE gel, the m.w. 84,000 molecule retained its capacity to suppress in vitro antibody production in an OVA-specific manner. From all these results it was concluded that this Ts cell factor may represent a soluble form of the alpha beta heterodimer of TCR of cloned Ts cells.

Regulation of RAG-1 and CD69 expression in the thymus during positive and negative selection

Successful interaction of the T cell receptor (TCR) with major histocompatibility complex (MHC) molecules during thymic selection down-regulates the expression of the recombination activating genes (RAG)-1 and -2 in cortical thymocytes and thereby prevents further endogenous TCR alpha-chain gene rearrangements (Borgulya, P., Kishi, H., Uematsu, Y. and von Boehmer, H., Cell. 1992. 69: 529-537; Brändle, D., Müller, C., Rülicke, T., Hengartner, H. and Pircher, H., Proc. Natl. Acad. Sci. USA 1992. 89: 9529-9533). To address the question whether down-regulation of RAG-1 activity represents an irreversible process we have blocked TCR-MHC interactions of thymocytes with thymic stromal cells. Firstly, transgenic (Tg) mice expressing a virus-specific MHC class I (H-2Db)-restricted TCR were injected with anti-Db or anti-CD8 monoclonal antibodies and RAG-1 expression was examined by in situ hybridization on thymus sections. The results show that cortical thymocytes up-regulated RAG-1 expression within 24 h after antibody administration. Secondly, immature thymocytes from TCR Tg mice were released from the thymic microenvironment and cultured in vitro for 14 h in single-cell suspension. The amount of RAG-1 mRNA was increased sixfold in cultured cells when compared to freshly isolated thymocytes. In addition, we show that immature thymocytes from TCR transgenic mice bearing non-selective MHC molecules (H-2d) down-regulated RAG-1 expression after antigen-induced TCR engagement. Cytofluorometric analysis further revealed that surface expression of CD69 on immature thymocytes inversely correlated with RAG-1 expression during positive and negative selection processes.

Donor-specific skin transplants activate allodestructive T cells in mice resistant to neonatal H-2 tolerance induction

Mice of the B10 background that are class II I-E nonexpressing demonstrate a relative resistance to neonatal induction of tolerance of class I alloantigens from I-E-expressing B10 strains. The majority of these injected mice delete donor-responsive and "I-E-reactive" (V beta 11+) cells in the immediate postinoculation period, with many remaining deleted of donor-specific T cells before the application of the test skin graft. Utilizing a hemisplenectomy technique in B10.S (I-E-) mice that received as neonates MHC-disparate (B10.SxB10.A)F1 (I-E+) lymphohematopoietic cells, we determined the proportion of adult mice that demonstrated pretransplant donor cell chimerism as well as several functional and phenotypic features ascribed to donor responsiveness. Surprisingly, chimeric cells were present in the bulk of recipients and many also exhibited a deletion of V beta 11+ T cells and a lack of alloreactivity to the donor strain allotype. Since chimeric, MLR-, V beta 11-deleted mice would be predicted to be tolerant to allograft challenge, we hypothesized that the test skin graft applied in adulthood was providing stimulatory signals that overcame this state of immunologic unresponsiveness. To examine this issue, injected mice that had been evaluated before skin grafting were challenged with donor-specific skin and evaluated for the same parameters measured in the pretransplant period. The majority (95%) of these mice subsequently rejected the B10.A skin graft in a range of 7-14 days. After graft rejection, V beta 11+ cell levels generally increased and chimeric cells were typically eliminated. Thus, the ability to reject allografts is not predicted by a "nonresponsive" immune phenotype or the presence of chimeric cells before application of the test allograft. In fact, the graft appears to provide an in vivo stimulus to the reduced numbers of host donor-specific T cells that results in the removal of chimeric cells and a breakdown of the tolerant state. We conclude that application of orthotopic skin grafts provides the signal(s) necessary to break class I tolerance induced neonatally in the context of I-E disparity.

Prevention of induction of unresponsiveness to class I antigens by veto activity of donor marrow in cylophosphamide-treated mice

The survival of skin grafts from B6.C-H-2bm1 (bm1; Kbm1,IAb,IE-,Db) mice was prolonged when C57BL/6 CrSlc (B6; H-2b) mice were inoculated intravenously with 9 x 10(7) spleen cells (SC) plus 3 x 10(7) bone marrow cells from bm1 mice 14 days prior to skin grafting. When B6 mice were inoculated i.v. with bm1 cells and treated intraperitoneally with 200 mg/kg cyclophosphamide (CP) 2 days later, the survival of bm1 skin grafts was not prolonged at all, suggesting antagonism between the veto cell-mediated enhancement by donor cells and CP-induced enhancement. In order to deplete the veto cells from the tolerogen, SC plus BMC were treated with anti-Thy1.2 mAb+C' or CP. The survival of the bm1 skin grafts was not prolonged at all in B6 mice inoculated with Thy1.2-treated bm1 or bm1 cells from CP-treated donors. When B6 mice were inoculated with Thy1.2-treated or CP-treated bm1 cells and followed by CP treatment, however, the survival of bm1 skin grafts was prolonged moderately. These results strongly suggested that the unresponsiveness induced with donor-derived veto cells prevents the tolerance induction to class I alloantigens (H-2Kbm1) by our protocol of CP-induced tolerance. Furthermore, in B6 mice injected with anti-Thy1.2 mAb on day -1 and bm1 cells on day 0, the survival of bm1 skin grafts was not prolonged at all. However, skin graft tolerance to bm1 antigens was induced when B6 mice were injected with anti-Thy1.2 mAb on day -1 and bm1 cells on day 0 followed by CP on day 2. These results may also be explained by the depletion of donor-derived veto cells in the recipient mice.

An endogenously synthesized decamer peptide efficiently primes cytotoxic T cells specific for the HIV-1 envelope glycoprotein

The immunodominant H-2Dd-restricted cytotoxic T lymphocyte (CTL) response to the HIV-1 gp160 envelope glycoprotein maps to a single determinant in the V3 loop, designated p18. Using a series of peptides synthesized on pins we have determined that the minimal core sequence of this determinant required for CTL recognition comprises 8 amino acids (residues 320-327). However, 9mer and 10mer peptides containing this core sequence were more effective than the 8mer peptide at sensitizing Dd-expressing target cells. To analyze the antigenicity of endogenously synthesized p18, minigenes encoding a 10-amino acid determinant (residues 318-327) and a 67-amino acid peptide (residues 281-348; containing the V3 loop) were expressed using vaccinia virus (Vac) recombinants. Both peptides were as effective as wild-type gp160 in their ability to sensitize target cells for lysis by gp160-specific CTL. Immunization of BALB/c mice with Vac recombinants encoding both gp160 peptides elicited gp160-specific CTL. These data demonstrate that both the V3 loop itself and a 10-residue epitope are sufficient to prime CTL in vivo and strongly support the potential use of minigene-encoded CTL epitopes for recombinant vaccines designed to induce protective T cell-mediated immunity against HIV-1.

In vivo administration of major histocompatibility complex class I-specific peptides from influenza virus induces specific cytotoxic T cell hyporesponsiveness

We have been investigating the immunogenicity of two class I major histocompatibility complex-specific peptides with a sequence derived from influenza virus nucleoprotein specific for Kd and one for Db. Peptide-modified splenocytes are unable to immunize for a primary cytotoxic T (Tc) cell response in vivo, or secondary response in vitro. Peptide-modified stimulator cells can boost virus-primed splenocytes for a strong secondary response in vitro. Animals primed with syngeneic peptide-modified splenocytes upon challenge with virus in vivo do not generate strong secondary Tc cell responses on day 3 after challenge in contrast to virus primed animals. Day 6 responses of virus-challenged, peptide-primed animals are reduced as compared to unprimed mice. This hyporesponsiveness is independent of CD8+ T cells in the priming population and can be elicited with tumor cell lines. The data are discussed in the framework of the two-signal model of immune induction.

Fewer protective cytotoxic T-cell epitopes than T-helper-cell epitopes on vesicular stomatitis virus

Cytotoxic T-lymphocyte (CTL) and T-helper-cell responses in various mouse strains were monitored. Protective CTL responsiveness against three proteins of vesicular stomatitis virus was H-2 linked and inducible only in half of the 15 combinations tested (each of five H-2 haplotypes combined with each of three viral proteins), whereas biologically relevant T-helper-cell responses were inducible in all. This suggests that vesicular stomatitis virus exhibits more T-helper-cell than CTL epitopes.

Pinealectomy ameliorates collagen II-induced arthritis in mice

To extend our previous findings that exposure to constant darkness (stimulation of endogenous melatonin release) as well as treatment with exogenous melatonin magnifies the severity of collagen-induced arthritis in mice, we have examined the effects of melatonin cutback by removing the pineal gland. Two strains of mice, DBA/1 and NFR/N, were subjected to surgical pinealectomy. The melatonin levels in sera were reduced by approximately 70% by the pinealectomy compared with the corresponding sham-operated controls. After 3-4 weeks of rest the mice were immunized with rat type II collagen to induce autoimmune arthritis, and the animals were kept in constant darkness during the experiments. In comparison with the controls, all groups of pinealectomized mice showed reduced severity of the arthritis by means of (i) a slower onset of the disease, (ii) a less severe course of the disease (reduced clinical scores), and (iii) reduced serum levels of anti-collagen II antibodies. These effects were not significant in all experiments, but the trends were always the same. Thus, the present result strengthen the hypothesis that high physiological levels of melatonin (which can be induced by exposure to darkness) stimulate the immune system and cause exacerbation of autoimmune collagen II arthritis, while inhibition of melatonin release (pinealectomy or exposure to light) has a beneficial effect.

Analysis of the genetic control of antibody response to Actinobacillus actinomycetemcomitans by immunoblotting inbred strains of mice

Genetic regulation of the immune response may be involved in the onset and progression of an early-onset type of periodontitis. We analyzed the genetic control of the primary antibody response to Actinobacillus actinomycetemcomitans in inbred strains of mice using an immunoblot technique. Mice of 5 independent inbred strains, 6 H-2 congenic strains and 4 B10 intra-H-2 recombinant strains were immunized with sonicated extracts of A. actinomycetemcomitans. On the seventh day their sera were examined for reactivity to the antigenic components of this organism. Western blot analysis clearly distinguished 2 different groups of antigens, one consisting of common antigens (molecular weights, 28, 34, 36 and 40 kDa) that reacted with sera from all strains and one consisting of specific antigens (molecular weights 31, 65 and 69 kDa) that reacted only with sera from distinct strains. Blot analysis of sera from H-2 congenic strains demonstrated that the reactivity to the second group of antigens was regulated by the H-2 complex. In B10 intra-H-2 recombinant strains, only the I-Ab allotype strains produced immunoglobulin G antibody that reacted to the 65 kDa antigen. This evidence indicates that the primary immune response to the A. actinomycetemcomitans antigen with a molecular weight of 65 kDa is controlled by genes in the I-A subregion of the H-2 complex. This 65 kDa antigen was also highly reactive with some human sera from early-onset periodontitis patients. Further analysis of this antigen is required.

Two novel vitamin D analogues, KH 1060 and CB 966, prolong skin allograft survival in mice

KH 1060 and CB 966, two novel analogues of 1,25-dihydroxyvitamin D3(1,25(OH)2D3), were found to significantly delay the rejection of allogeneic skin grafts in CBA (H-2k) recipient mice, transplanted with skin from C57Bl/6 (H-2b) donor mice. Graft survival was assessed in mice treated with KH 1060 or CB 966 until the day of rejection, in comparison to mice treated with vehicle, 1,25(OH)2D3 or cyclosporin A (CsA). The mean graft survival time in days was found to be: 16.6 +/- 0.5 (CsA, 20 mg/kg/day orally (p.o.); 13.9 +/- 0.6 and 15.5 +/- 0.6 (1,25(OH)2D3, 0.2 and 0.4 microgram/kg/day intraperitoneally (i.p.)); 14.3 +/- 0.2 and 18.7 +/- 0.5 (CB 966, 0.2 and 0.4 microgram/kg/day i.p.); 13.7 +/- 0.8, 15.7 +/- 1.7, 18.2 +/- 2.7 and 24.5 +/- 0.5 (KH 1060, 0.02, 0.1, 0.2 and 0.4 microgram/kg/day i.p.). Mean graft survival in days for control mice was: 10.3 +/- 0.2 (vehicle for injection, i.p.) and 11.5 +/- 0.2 (olive oil, p.o.). Serum calcium levels, measured on the day of rejection, rose moderately after treatment with either KH 1060 or CB 966. Combination of CsA (20 mg/kg/day p.o.) with KH 1060 (0.1 microgram/kg/day i.p.) resulted in an additive or synergistic effect: 23.4 +/- 1.1 days of skin allograft survival, compared to 15.7 +/- 1.7 days with KH 1060 alone, and 15.1 +/- 1.9 days with CsA alone. KH 1060 was the most active of the tested compounds and can therefore be regarded as a potent immunosuppressor in transplantation; it can be used in combination with CsA and is effective at doses which only marginally affect serum calcium levels.

The cytolytic activity of pulmonary CD8+ lymphocytes, induced by infection with a vaccinia virus recombinant expressing the M2 protein of respiratory syncytial virus (RSV), correlates with resistance to RSV infection in mice

Previous studies demonstrated that the pulmonary resistance to respiratory syncytial virus (RSV) challenge induced by immunization with a recombinant vaccinia virus expressing the M2 protein of RSV (vac-M2) was significantly greater 9 days after immunization than at 28 days and was mediated predominantly by CD8+ T cells. In this study, we have extended these findings and sought to determine whether the level of CD8+ cytotoxic T-lymphocyte (CTL) activity measured in vitro correlates with the resistance to RSV challenge in vivo. Three lines of evidence documented an association between the presence of pulmonary CTL activity and resistance to RSV challenge. First, vac-M2 immunization induced pulmonary CD8+ CTL activity and pulmonary resistance to RSV infection in BALB/c (H-2d) mice, whereas significant levels of pulmonary CTL activity and resistance to RSV infection were not seen in BALB.K (H-2k) or BALB.B (H-2b) mice. Second, pulmonary CD8+ CTL activity was not induced by infection with other vaccinia virus-RSV recombinants that did not induce resistance to RSV challenge. Third, the peak of pulmonary CTL activity correlated with the peak of resistance to RSV replication (day 6), with little resistance being observed 45 days after immunization. An accelerated clearance of virus was not observed when mice were challenged with RSV 45 days after immunization with vac-M2. The results indicate that resistance to RSV induced by immunization with vac-M2 is mainly mediated by primary pulmonary CTLs and that this resistance decreases to very low levels within 2 months following immunization. The implications for inclusion of CTL epitopes into RSV vaccines are discussed in the context of these observations.

Murine systemic autoimmune disease induced by mercuric chloride (HgCl2): Hg-specific helper T-cells react to antigen stored in macrophages

The adoptive transfer popliteal lymph node assay (PLNA) was used to demonstrate Hg-specific T-cell responses of mice that were continuously treated with HgCl2 by a regimen known to induce a systemic autoimmune disease in H-2s (murine histocompatibility complex, haplotype s) mice, but not H-2d mice. We found that spleen cells of B10.S and A.SW donors (both H-2s) responded anamnestically to HgCl2 by inducing a significant increase in cellularity in the draining PLN of the recipient: In contrast, spleen cells of HgCl2-treated DBA/2 (H-2d) donors failed to induce an increase in PLN cellularity, and spleen cells of B10.D2/n (H-2d) donors induced no changes or even diminished PLN cellularity upon re-encounter with HgCl2. Kinetic studies showed that spleen cells of B10.S donors were stimulatory from day 3 until day 14 of donor HgCl2 treatment and, when purified splenic T-cells were tested, still on day 28, the last point in time tested. The Hg-specific T-cells prepared from HgCl2-treated B10.S mice not only induced an increased cellularity, but also B-cell activation to antibody secretion in the draining PLN of the recipient. Moreover, the Hg-specific donor T-cells transferred could specifically be restimulated by killed peritoneal cells obtained from the same donors or from syngeneic donors previously treated with HgCl2. Interestingly, when killed peritoneal cells were injected as antigen the amount of Hg required for T-cell restimulation was only 1/40 of that required when free HgCl2 was used. Taken together, these results show that an HgCl2 treatment schedule designed to induce systemic autoimmune disease primes Hg-specific T-helper (Th) cells and generates immunogenic material in peritoneal cells to which the T-cells react. The possible contribution to the pathogenesis of HgCl2-induced auto-immune disease of these Hg-specific T-cells and the autoreactive T-cells reported in the literature is discussed.

Purified MHC class I molecules present hapten-conjugated peptides to TNP/H-2Kb-specific T cell hybridomas

Several trinitrophenyl (TNP)-specific mouse cytotoxic T cell (CTL) clones recognize TNP-conjugated peptides in association with class I MHC Kb-molecules. Here we show that CD8+ T cell hybridomas derived from these CTL exhibit the same pattern of antigen-specificity as their parent CTL-clones. These T cell hybridomas reacted with TNBS- or TNP-peptide modified syngeneic target cells, and also with affinity purified, immobilized Kb-molecules preloaded with TNP-peptides. These findings demonstrate most directly that MHC-associated, haptenated peptides create functional antigenic epitopes for TNP-specific CTL. Furthermore, using purified Kb-molecules and a panel of Kb-binding TNP-conjugated peptides, we demonstrated that the epitope density is a critical factor in triggering these T cell hybridomas. Chemical modification of immobilized Kb-layers resulted in poor antigenicity, implying low epitope density and therefore arguing against covalent MHC-haptenization as a major source of T cell antigenic determinants.

Susceptibility to measles virus-induced encephalitis in mice correlates with impaired antigen presentation to cytotoxic T lymphocytes

In measles virus (MV) infection in humans, meningitis and encephalitis are important complications. However, little is known of the pathogenesis of MV encephalitis, in particular about the role of the immune response. We have examined the role of cytotoxic T lymphocytes (CTL) in a mouse model of MV-induced encephalitis. We report here that the resistance of inbred strains of mice to MV-induced encephalitis correlated with the major histocompatibility complex (MHC) haplotype and that only resistant mouse strains mounted an effective CTL response to MV. Mice with low susceptibility to MV infection, such as the BALB/c strain (H-2d), generated CTL, whereas the highly susceptible strains, C3H (H-2k) and C57BL/6 (H-2b), revealed very poor CTL responses. MV-induced CTL were usually CD8+, and the generation of these cells was independent of the route of inoculation or the time postinfection. CD4+ T cells were generally only weakly lytic. The nucleocapsid protein was the major target antigen for CTL in BALB/c mice, although in some experiments the hemagglutinin was also recognized. CTL from C3H and C57BL/6 mice did not lyse MV-infected target cells. However, targets infected with vaccinia virus recombinants expressing the nucleocapsid protein or hemagglutinin were lysed, but levels of cytotoxicity were still low. Experiments using target cells transfected with single MHC class I genes suggested inefficient antigen presentation of MV proteins by the MHC molecules of the H-2k and H-2b haplotypes.

Molecular mimicry by major histocompatibility complex molecules and peptides accounts for some alloresponses

One explanation offered for the uniquely high precursor frequencies of T cells which recognize allogeneic major histocompatibility complex (MHC) molecules, and their lack of self-MHC restriction, is that the alloreactive cells are polyclonal populations the primary specificity of which is self-MHC plus peptide X1, X2, ... Xn. These are postulated to cross-react with allo-MHC plus peptides Y1, Y2, ... Yn. It has been further suggested that the structural basis for the crossreactivity between different MHC alleles is the similarity in amino acid sequence of that part of the molecule predicted to make contact with the T cell receptor (TcR). In order to test this concept, T cells were obtained with dual specificity for influenza haemagglutinin (HA), restricted by HLA-DR1Dw1, and for DR4Dw4/Dw14 expressed on allogeneic human B cell lines, and the specificity of one clone was studied in detail. The exposed, TcR-contacting surfaces of these two DR molecules are predicted to be identical. Although the HA-specific response was stimulated by DR1-expressing mouse DAP.3 transfectants, DAP.3 cells expressing the alloantigen DR4Dw4 were unable to stimulate, possibly because of a failure to present the necessary human peptide for anti-DR4 allorecognition. Therefore, the effects of pulsing the DR4Dw4-expressing DAP.3 cells with the HA peptide were examined. This peptide is known to bind to both DR1 and DR4. Addition of the HA peptide restored the anti-DR4Dw4 response. These data support the concept that allorecognition in some responder/stimulator combinations can be explained by cross-reactivity at the level of the MHC molecule and the peptide.

Anti-TCR-V beta 6 breaks tolerance in female AKR, Mlsa mice inducing foetal lethality

Immunisation with anti-TCR-V beta 6 of female AKR mice prior to and during syngeneic pregnancy resulted in neonatal lethality and eventually in abortion or foetal resorption. The sera of the hyperimmunised mothers were shown to have anti-H-2k and anti-Mlsa autoantibodies and were cytotoxic to H-2k targets in vitro and also blocked Mlsa-induced mixed lymphocyte reactions. These observations are discussed herein.

The unique killing of embryo-derived teratocarcinoma cells by nonactivated murine macrophages is not due to a lack of H-2 antigen expression

It is well documented that activated macrophages, but not nonactivated ones, kill tumor cells in vitro without damaging normal cells. We, however, have previously shown that embryo-derived teratocarcinoma cells (F9, P19, PCC4) are efficiently killed by nonactivated macrophages as well as by activated ones. Whereas other tumor cells are killed extracellularly by macrophages, we found that F9 teratocarcinoma cells are phagocytosed alive by macrophages and subsequently killed intracellularly by a process dependent on intact lysosomal function. Neither the H-2 antigens nor the mRNAs for the alpha-chain and beta 2-microglobulin are detectable in embryo-derived teratocarcinoma cells. An obvious explanation for this unique killing is that the nonactivated macrophages recognize and kill these cells due to their lack of class I MHC antigen expression, assuming that class I MHC gene products on the target cells switch off the cytolytic machinery of nonactivated macrophages. Our present findings demonstrate that there is no correlation between H-2 antigen expression on tumor cells and their susceptibility to killing by macrophages. Retinoic acid-differentiated F9 cells and P19 cells expressing H-2 antigen after exposure to MAF (IFN-gamma) were sensitive to the killing by nonactivated macrophages. Hybrids that arose from fusion of P19 teratocarcinoma cells with embryonal normal fibroblasts (C57BL/6), which displayed the morphology of embryonal carcinoma stem cells and expressed H-2 antigens, were also sensitive to the killing by nonactivated macrophages. On the other hand, the H-2-negative testicular 402AX teratocarcinoma cells and K1735P melanoma cells were both resistant to the killing by nonactivated macrophages. We concluded that the unique killing of embryo-derived teratocarcinoma cells by nonactivated murine macrophages is not related to a lack of H-2 antigen expression.

Further evaluation of the pregnancy-linked down-regulation of the paternal antigen-specific splenic cytotoxic T lymphocyte activity in allogeneically pregnant mice

Cytotoxic T lymphocyte (CTL) activity directed against paternal alloantigen was examined in allogeneically pregnant mice using various allogeneic combinations. The spleen cells from pregnant C57BL/6 (H-2b) mice mated with BALB/c (H-2d) male mice generated less anti-H-2d CTL after in vitro sensitization than those from unpregnant or syngeneically mated C57BL/6 mice. Different allogeneic combinations including the incompatibility at only D region of H-2 or minor histocompatibility loci were effective for downregulating the anti-paternal CTL activity in pregnancy. The downregulation of anti-paternal CTL activity induced by allogeneic pregnancy occurred at day 10 to day 18 of pregnancy, most extensively at day 14. The allogeneic pregnancy also downregulated the allogeneic CTL activities that had been amplified by injecting alloantigens before mating.

Alternative patterns of MHC-restricted antibody responsiveness following intraperitoneal immunization of inbred mice with different preparations of an 86 kilodalton antigen of Schistosoma mansoni

The investigation of MHC restricted antibody responses to an 86 kDa antigen (p86) during chronic Schistosoma mansoni infection has been extended to immunization with this antigen. In the absence of adjuvant, a similar pattern of responsiveness by mice expressing H-2k and H-2d but not H-2b was observed following immunization with unpurified adult worm homogenate. Adjuvant selectively abrogated the capacity of H-2d mice to respond and this was also the case when purified p86 with adjuvant was injected. Immunization with purified subfragments of p86 again demonstrated MHC restriction in the capacity to immunoprecipitate p86 in vitro translation product, the pattern varying according to the fragment used. Western blot analysis showed that in some, but not all instances of apparent 'non-responsiveness' characterized by immunoprecipitation, antibody specificities capable of recognizing p86 epitopes on the nitrocellulose bound p86 were, indeed, present. Thus the fine specificity as well as the absolute capacity to respond is influenced by both the MHC haplotype of the host and the nature of the immunizing antigen.