Positive and negative selection of T cell repertoires during differentiation in allogeneic bone marrow chimeras

T cells acquire immune functions during expansion and differentiation in the thymus. Mature T cells respond to peptide antigens (Ag) derived from foreign proteins when these peptide Ag are presented on the self major histocompatibility complex (MHC) molecules but not on allo-MHC. This is termed self-MHC restriction. On the other hand, T cells do not induce aggressive responses to self Ag (self-tolerance). Self-MHC restriction and self-tolerance are not genetically determined but acquired a posteriori by positive and negative selection in the thymus in harmony with the functional maturation. Allogeneic bone marrow (BM) chimera systems have been a useful strategy to elucidate mechanisms underlying positive and negative selection. In this communication, the contribution of BM chimera systems to the investigation of the world of T-ology is discussed.

Neuronal changes in the arcuate and hypoglossal nuclei of brain stem induced by head injury

In head injury, assessing the damage not only to the cerebrum and the cerebellum but also to the brain stem is very important. In this paper, we report neuronal changes of the arcuate nucleus (ARC) and the hypoglossal nucleus (HN) in the brain stem. We investigated these changes immunohistochemically with antibodies against microtubule-associated protein 2 (MAP2), muscarinic acetylcholine receptor (mAChR), c-fos gene product (c-Fos), and the 72 kD heat-shock protein (HSP70). We measured the percentage of immunopositive neurons among the total neurons of the ARC and the HN. The investigation of neuronal changes in relation to the type of head injury showed different results. In cases of tonsillar herniation, immunoreactivity to MAP2 and mAChR in the ARC was significantly lower than in the HN (p < 0.01). Moreover, MAP2, HSP70 and c-Fos reactivities in the ARC were significantly lower than in other types of head injuries (p < 0.01). In the HN, diffuse axonal injury produced slightly higher immunoreactivity to mAChR and c-Fos (p < 0.1). Our observations indicate that immunohistochemical examination of brain stem nuclei can provide useful information for estimating damage to the brain stem.

Effect of toluene inhalation on astrocytes and neurotrophic factor in rat brain

Toluene, an abused substance in Japan, is a neurotoxic chemical that has been shown to have neurobehavioral and electrophysiological effects. In previous work, both acute and chronic effects of toluene on cells have been studied extensively. However, although glial cells are thought to play an important role in the survival of neurons in the brain, the effect of toluene on glial cell function has not yet been characterized. To elucidate this, the effect of toluene inhalation on astrocytes in rat brain was examined. Toluene exposure (1500 ppm for 4 h on 4-10 days) augmented glial fibrillary acidic protein (GFAP) immunoreactivity, particularly in the hippocampus and cerebellum. Quantitative analysis showed that toluene inhalation markedly enhanced GFAP expression in the hippocampus and cerebellum. In both regions, proliferating cell nuclear antigen (PCNA) showed no obvious changes, but glutamine synthetase (GS)-immunoreactive cells were markedly increased by toluene exposure. Thus, the elevation of GFAP expression was induced by astrocyte activation rather than by cell proliferation. If toluene exposure activates astrocytes, astrocytes may play a role in the neurophysiological changes observed in toluene intoxication. A neurotrophic factor, basic fibroblast growth factor (b-FGF) was observed immunohistochemically in the capillary vessel walls in the hippocampus and the cerebellum of toluene-intoxicated rats. Basic-FGF may have induced GFAP expression both in the hippocampus and the cerebellum. So, other neurotrophic factors may affect the difference of GFAP elevation between the hippocampus and the cerebellum. These differences may relate to neurobehavioral function of each brain part after toluene exposure.

Elevation of steroid 5 alpha-reductase mRNA levels in rat cerebellum by toluene inhalation: possible relation to GFAP expression

Toluene, a commonly used industrial solvent, is known to be toxic to both neuronal and glial cells, and has been shown to increase the immunoreactivity of glial fibrillary acidic protein (GFAP) in the brain. However, the mechanism of toluene-induced GFAP expression is poorly understood. Recently, GFAP mRNA expression in cultured astrocytes has been shown to be modulated by various steroid hormones, such as progesterone, testosterone, and their 5 alpha-reduced metabolites. Therefore, it seems possible that steroid hormones may play a potential role in the enhancement of GFAP expression observed following toluene exposure. To address this possibility, the effect of toluene inhalation on the expression of mRNAs encoding GFAP and steroidogenic enzymes in rat brain was examined. Toluene exposure increased GFAP protein contents without any significant alteration in GFAP mRNA levels in the hippocampus. In contrast, the elevation of both GFAP protein contents and its mRNA levels was observed in the cerebellum following toluene exposure. Further studies indicated that toluene exposure increased steroid 5 alpha-reductase (5 alpha-R) mRNA levels prior to the elevation of GFAP mRNA in the cerebellum, whereas neither 5 alpha-R nor GFAP mRNA levels in the hippocampus were significantly affected by toluene exposure. These results suggest that toluene inhalation may enhance GFAP gene expression in the rat cerebellum, and propose the possibility that the elevation of 5 alpha-R expression, and hence 5 alpha-reduced metabolites of steroid hormones, is presumably related to toluene-induced GFAP mRNA expression.

Enhancement of glial cell line-derived neurotrophic factor expression in rat adrenal glands by toluene exposure

Toluene, a widely used industrial organic solvent, has been shown to influence the function of catecholaminergic cells including sympathoadrenergic neurons and adrenal medullary cells. While glial cell line-derived neurotrophic factor (GDNF), a member of the transforming growth factor-beta superfamily, has recently been shown to be expressed in rat adrenal glands, and suggested as playing a potential autocrine or paracrine role in development and differentiation of the adrenal medullary cell. Based on these findings, it seemed of interest to examine the effect of toluene exposure on GDNF expression in the adrenal medulla. Toluene inhalation (1500 ppm for 4h on 4-10 days) increased GDNF protein content in rat adrenal glands without any significant change in GDNF mRNA level. Furthermore, toluene exposure failed to cause any notable change in the expression of mRNA encoding phenylethanolamine N-methyltransferase (PNMT), a stress-inducible enzyme in the adrenal medulla. These results suggest that the elevation of GDNF protein expression caused by toluene exposure is likely due to the enhancement of protein synthesis and/or processing rather than the stimulation of GDNF gene transcription in rat adrenal glands, and may not be directly associated with the stress response of adrenal glands during toluene inhalation.

HSP70 and c-Fos expression of brain stem hypoglossal nucleus in drowning

The brain stem hypoglossal nucleus (HN) is the center of nerves innervating the upper respiratory tract and is related to control of mastication, deglutition, speech and respiration. To elucidate the relationship between asphyxia and the HN, we investigated the change of hypoglossal neurons in cases of hanging, strangulation, smothering, choking, drowning and respiratory failure. Using immunohistochemical techniques, we observed the brain stem HN with antibodies against microtubule-associated protein 2 (MAP2), muscarinic acetylcholine receptor (mAChR), c-fos gene product (c-Fos) and 72 kD heat-shock protein (HSP70). MAP2, a cytoskeletal protein of the neuron, is a marker of neuronal damage. Muscarinic AChR was used as a marker of neuronal membrane and ACh signaling. We employed both HSP70 and c-Fos as markers of stress- or damage-related events. We measured the percentage of immunopositive neurons in total neurons of HN. Drowning produced higher expression of HSP70 and c-Fos than other causes of asphyxia, suggesting that drowning induces more severe damage in HN neurons. Furthermore, it was suspected that neuronal changes in drowning might relate to functions of the HN. These observations indicate that immunohistochemical examination of the brain stem HN could provide useful information for determining the cause of asphyxia.

[Immunohistochemical studies on neuronal changes in brain stem nucleus of forensic autopsied cases. II. Sudden infant death syndrome]

Several nuclei in brain stem are well known to play an important role in supporting human life. However, the connection between neural changes of brain stem and the cause of death is not yet fully understood. Previously, in sudden infant death syndrome (SIDS) it has been suggested that impaired cardioventilatory control might contribute to cause of death. So, to investigate the brain stem damage in SIDS, neural changes of the arcuate nucleus (ARC), the hypoglossal nucleus (HN) and the inferior olivary nucleus (IO) was examined using immunohistochemical technique. Brain was fixed with phosphate-buffer formalin, and the brain stem was horizontally dissected at the level of apex, then embedded in paraffin. The sections were stained with the antibodies against microtubule-associated protein 2 (MAP2), muscalinic acetylcholine receptor (mAChR), c-fos gene product (c-Fos) and 72 kD heat-shock protein (HSP70). Morphological changes of neurons in three nuclei were not evident. Moreover, because MAP2 degeneration and expression of HSP70 and c-Fos were not observed, neuronal damage in those nuclei was not suspected. However, although there was no abnormality of mAChR immunostaining in HN and IO, the rate of mAChR-immunopositive neurons in ARC was less than that in control. These observations indicate that immunohistochemical study on the neuronal changes in ARC can provide useful information for diagnosing SIDS.

[Immunohistochemical studies on neuronal changes in brain stem nucleus of forensic autopsied cases. I. Various cases of asphyxia and respiratory disorder]

Several nuclei in brain stem are well known to play an important role in supporting human life. However, the connection between neural changes of brain stem and the cause of death is not yet fully understood. To investigate the correlation of brain stem damage with various cause of respiratory disorders, neural changes of the arcuate nucleus (ARC), the hypoglossal nucleus (HN) and the inferior olivary nucleus (IO) were examined using immunohistochemical technique. Based on the cause of death, the forensic autopsy cases were divided into 5 groups as follows. Group I: hanging, ligature strangulation and manual strangulation, Group II: smothering and choking, Group III: drowning, Group IV: respiratory failure, control group: heat stroke and sun stroke. Brain was fixed with phosphate-buffer formalin, and the brain stem was horizontally dissected at the level of apex, then embedded in paraffin. The sections were stained with the antibodies against microtubule-associated protein 2 (MAP2), muscalinic acetylcholine receptor (mAChR), c-fos gene product (c-Fos) and 72 kD heat-shock protein (HSP70). Three nuclei showed no obvious morphological changes in all examined groups. However, in case of asphyxia (Group I to III), neurons in HN were positively stained with both HSP70 and c-Fos antibodies. This may indicate that the occlusion of upper airway results in the neuronal damage of HN without their morphological changes. Positive staining of HSP70 and c-Fos in IO was more frequently observed in Group III than other 4 groups. Since IO is involved in maintaining body balance which is often disturbed by drowning, it seems possible that neuronal damage in IO observed in drowning may be related to the disturbance of body balance. These observations indicate that immunohistochemical study on the damage to neurons in brain stem nuclei can provide useful information for determining the cause of death.

Comparative analyses of thymocyte and thymic low-density adherent cell functions

Thymocytes which have developed in the C3H thymus showed depressed proliferative responses to stimulation with anti-CD3 antibody as compared with those which have developed in the thymus of other strains of mice (i.e. AKR). The present study was conducted to analyze immunological functions of the thymic stromal cell population (low-density adherent cells, LDAC) in the C3H mice using allogeneic bone marrow (BM) chimeras established by BM transplantation in the reciprocal combination of AKR and C3H mice as donor or recipient. The thymic LDAC from C3H mice or the [AKR(donor)-->C3H(recipient)] chimeras contained a high proportion of Mac-1+ cells as compared to AKR mice or the [C3H-->AKR] chimeras. The proportion of Mac-1+ cells paralleled the IL-1- and PGE2-secreting ability of the LDAC cultured either in the presence or absence of LPS and also paralleled the antigen-presenting cell functions of the LDAC. Furthermore, after anti-CD3 stimulation the PGE2 inhibited more profoundly proliferative responses of [AKR-->C3H] or normal C3H thymocytes than those of the [C3H-->AKR] chimera or normal AKR thymocytes. A PGE2 inhibitor, indomethacin, reversed the depressed responses of the thymocytes which had developed in the C3H thymus. These findings suggest that the lower responsiveness of thymocytes from [AKR-->C3H] chimeras to anti-CD3 stimulation may be attributable to large amounts of PGE2 secreted by LDAC and/or to increased sensitivity of thymocytes themselves to PGE2.

Analysis of epitopic residues introduced into the hybrid peptide vaccines prepared according to the cassette theory

In our previous study, we prepared a synthetic peptide vaccine (46F/HA127-133/54A) against influenza strain A/Aichi/2/68 (H3N2) virus by introducing haemagglutinin (HA) 127-133 to an I-Ab,b binding component that consisted of residues 43-46 and 54-58 of an I-Ab,d binding peptide, 46F50V54A. This hybrid peptide vaccine induced considerable immunological responses against A/Aichi/2/68 as well as against the peptide vaccine in I-Ab mice. In the present study, we have attempted to increase the immunogenicity of the peptide vaccine by introducing HA peptides of various lengths into the I-Ab,d binding components consisting of residues 43-46 and 54-58 or 43-47 and 53-58 of 46F50V54A. We demonstrate here that, among the peptide vaccines prepared, 46F/HA127-133/54A (18 mer) consisting of HA127-133 and the I-Ab,d binding component constructed from 43-47 and 53-58 of 46F50V54A induces the most vigorous T-cell responses and neutralizing antibodies against A/Aichi/2/68 in both I-Ab and I-Ad mice.

Determination of amino acids on agretopes of pigeon cytochrome c-related peptides specifically bound to I-A allelic products

In our prior study it was demonstrated that residues 46 and 54 on a synthetic peptide, AEGFSYTVANKNKGIT (50V), work as an agretope (site contacts with major histocompatibility complex molecules) and residues 50 and 52 function as an epitope (site contacts with T cell receptor), when tri-molecular complexes are formed among 50V,I-Ab and the T cell receptor. 50V was composed of residues 43 to 58 of pigeon cytochrome c (p43-58) except that the aspartic acid (D) at residue 50 was substituted by valine (V). Substitution of agretopic residues on 50V changed this I-Ab-binding peptide to an I-Ak-binding peptide, suggesting that positions 46 and 54 work as an agretope in I-Ak-restricted T cell responses. In the present study we examined whether residues 46 and 54 of 50V worked as agretopes in T cell responses restricted to other I-A haplotypes. The 50V-related peptides with phenylalanine (F) at position 46 and alanine (A) at position 54 bound tightly to I-Ab, I-Ad, I-Aq and I-As molecules and stimulated T cells most potently in mice bearing these I-A haplotypes. In contrast, 50V-related peptides carrying D at position 46 and A at position 54 bound most potently to I-Ak molecules, and the peptides with arginine (R) at position 46 and A at position 54 bound most efficiently to I-Av molecules. The present findings, thus, demonstrate that the agretopic positions on the p43-58 related peptides are preserved in T cell responses restricted to each I-A haplotype studied, and that the specific amino acids on the agretopic positions exist a priori for each I-A allele-specific structure.

[Investigation of agretopic motifs in T cell responses specific for pigeon cytochrome c related peptides and restricted to I-E molecules]

In our previous study, epitopic and agretopic residues of a peptide fragment deduced from pigeon cytochrome c43-58 (p43-58, AEGFSYTDANKNKGIT) and it's analogues in the T cell responses restricted to I-A molecules were determined. It has been shown that amino acid residue position 50 of the p43-58 works as an epitopic which contacts with T cell antigen receptor (TCR) and residues at positions 46 and 54 function as agretopes which contact with I-A molecules. In the present study, epitopic and agbretopic sites were analyzed in T cell proliferative responses that were restricted to the other class II, I-E, molecules. A peptide antigen, 46D50V54R, which had been prepared by substitution of amino acids at positions 46, 50 and 54 of p43-58 with aspartic acid (D), valine (V) and arginine (R), respectively was shown to induce class II restricted T cell responses in B10. A (3R) (I-Ab, I-Eb/k) but not in B10 (I-Ab, I-E-) mice. Similarly, 50V50R which had been prepared by substitution of amino acids at positions 50 and 54 with V and R, respectively induced T cell proliferation in B10. BR mice (I-Ak, I-Ek) but not in B10. A (4R) (I-Ak, I-E-) mice. These findings indicate that the 46D50V54R and 50V54R generate I-E restricted proliferative responses of T lymphocytes in I-Eb/k and I-Ek-carrying mice, respectively. Furthermore, it was shown that residue 50 functions an an epitope and residues 46 and 54 as agretopes in the I-E restricted responses. Almost identical results were obtained when I-E restricted responses of T lymphocytes were analyzed in B10. PL (H-2u) and B10. SM (H-2v) mice. However, sine no I-E negative counterpart strain for these two latter strains is available, complete analysis concerning the epitopic and agretopic functions has not been performed with B10. PL and B10. SM mice. The present findings demonstrate that the functional sites of the p43-58 analogues are preserved is the T cell responses restricted to each I-E haplotype studied. However, when most potent agretopic motif was determined in various mouse strains, the specific amino acid motifs on the agretopic positions were different among various I-E haplotypes. Furthermore, substitution of the epitopic residue showed no influence on the binding affinity between agretopic residues and class II molecules. Thus, these epitope and agretopes appear to function independently.(ABSTRACT TRUNCATED AT 400 WORDS)

A strategy for making synthetic peptide vaccines

We have determined the H-2 class II allele-specific amino acid motif of the agretope (the site of contact between the peptide antigen and the major histocompatibility complex) for a synthetic peptide composed of residues 43-58 of pigeon cytochrome c (p43-58). Residues 46 and 54 functioned as the agretope, and residues 50 and 52 functioned as the epitope (the site for contact between the peptide antigen and the T-cell antigen receptor). In general, agretopes and epitopes function independently. Thus, substitution of amino acids in the epitope does not significantly affect binding of the peptide antigen to a class II molecule. On the basis of these findings, synthetic peptide vaccines against influenza Aichi (H3N2) virus were prepared by introducing seven residues of the influenza virus hemagglutinin into the frame component residues 43-46 and 54-58 of p43-58 analogues including the agretopes for Ak or Ab previously determined on the p43-58 segment. These peptide vaccines induced both helper T-cell responses and production of antibodies that were specific for influenza Aichi hemagglutinin but not for the major histocompatibility complex binding frame in mice bearing Ak or Ab. The antibodies produced neutralize the infectivity of influenza Aichi in vitro. The present findings should provide a basis for preparing potent peptide vaccines that function without producing side effects.

A hole in the T cell repertoire specific for a pigeon cytochrome c related peptide associated with amino acid substitutions on I-Ab molecules

When C57BL/10(B10) mice were immunized with a pigeon cytochrome c related peptide, 50V (AEGFSYTVANKNKGIT), two helper T cell populations with different specificity were activated. A major T cell population reacted with a 50V analog, 50V54A (AEGFSYTVANKAKGIT), more potently than with the immunogen, 50V, in a heteroclitic fashion, whereas the other minor T cell population responded only to 50V. By contrast, when bm12 mice were immunized with 50V, the minor T cell population responding only to 50V could hardly be demonstrated. The apparent deletion of the minor T cell population in bm12 mice seems to be attributable to negative selection under the influence of I-Abm12 molecules, since the minor T cell population was undetectable in both I-Ab and I-Abm12 restricted T cells from (B10 x bm12)F1 mice. Thus, three mutant points on the I-A molecule in bm12 mice appear to be involved in the seemingly negative selection of the certain T cell repertoire. The present finding demonstrates that a T cell repertoire generated under the influence of a MHC product (Ab) on one parental strain is eliminated by a different MHC product (Abm12) on the other parental strain of F1 cross. The mechanism underlying the apparent negative selection is discussed.

Analysis of functional sites on a peptide antigen, p43-58, in I-A or I-E-restricted T cell responses

It has been shown that two different sites (an agretope and an epitope) on a peptide antigen function independently in T cell responses to the antigen. By virtue of these sites, antigens, MHC molecules, and TCRs constitute trimolecule complexes which eventually result in T cell activation. In our previous reports, we have defined that residues 46 and 54 on synthetic peptide composed of residues 43-58 of pigeon cytochrome c (p43-58, AEGFSYTDANKNKGIT) and its analogs function as an agretope and residue 50 as an epitope in both I-Ab and I-Ak-carrying mice. In the present study, to extend our method to the other MHC class II molecules (I-E), we used two peptide antigens, 46D50V54R and 50V54R, which had been prepared by substitution of amino acids at positions, 46, 50 and 54 or 50 and 54 of p43-58 D, V, R or V, R, respectively, and compared the immunogenicity with those of other peptide analogs. The 46D50V54R was shown to be non-immunogenic in I-Ab-carrying mice and the 50V54R was non-immunogenic in I-Ak-carrying mice. In contrast, the 46D50V54R or 50V54R could induce I-E-restricted proliferative responses of T lymphocytes in I-Eb/k- or I-Ek/k-carrying mice, respectively. Furthermore, residues 46 and 54 were shown to function as agretopes and residue 50 as an epitope in the I-E-restricted responses as they did in the I-A-restricted responses, even though some differences were seen between peptide-I-E interaction and peptide-I-A interaction. These agretopes and epitope functioned independently.

Thymus: a direct target tissue in graft-versus-host reaction after allogeneic bone marrow transplantation that results in abrogation of induction of self-tolerance

Graft-versus-host reaction (GVHR) following allogeneic bone marrow (BM) transplantation was investigated by analyzing expression of antigen receptors on T cells specific for recipient antigens. GVHR chimeras were prepared by transplanting mixtures of splenic T cells and T-cell-depleted BM cells from B10 (I-E-, Mls-1b) or B10.AQR (I-E+, Mls-1b) mice into lethally irradiated AKR/J (I-E+, Mls-1a) recipients. Increased proportions of V beta 6+ T cells reactive to recipient antigens (I-E and Mls-1a) were observed in thymuses from such chimeras 1 or 5 wk after BM transplantation. V beta 6+ T cells observed 1 wk after BM transplantation were derived from mature T cells that had been inoculated into recipients. These cells responded to recipient antigens expressed in the thymus. After 5 wk, thymocytes brightly positive for V beta 6+ were shown not to descend from mature T cells but to differentiate from precursor cells present in the BM inocula. Since V beta 6+ T cells were eliminated in thymuses from non-GVHR chimeras 5 wk after BM transplantation using T-cell-depleted BM cells alone, it appears that GVHR occurring in the thymus at an early stage abrogates thymic stromal functions essential to induction of self-tolerance in the T-cell repertoire. These findings propose a mechanism (autoimmunity) to explain in part the pathogenesis of chronic GVHR.

Apolipoprotein E and lipoprotein lipase secreted from human monocyte-derived macrophages modulate very low density lipoprotein uptake

We investigated the roles of lipoprotein lipase and apolipoprotein E (apoE) secreted from human monocyte-derived macrophages in the uptake of very low density lipoproteins (VLDL). ApoCII-deficient VLDL were isolated from a patient with apoCII deficiency. The lipolytic conversion to higher density and the degradation of the apoCII-deficient VLDL by macrophages were very slight, whereas the addition of apoCII enhanced both their conversion and degradation. This suggests that the lipolysis and subsequent conversion of VLDL to lipoproteins of higher density are essential for the VLDL uptake by macrophages. VLDL incubated with macrophages obtained from subjects with E3/3 phenotype (E3/3-macrophages) showed a 17-fold greater affinity in inhibiting the binding of 2 micrograms/ml 125I-low density lipoprotein (LDL) to fibroblasts than native VLDL, whereas the incubation of VLDL with macrophages obtained from a subject with E2/2 phenotype (E2/2-macrophages) did not cause any increase in their affinity. Furthermore, 3 micrograms/ml 125I-VLDL obtained from a subject with E3/3 phenotype were degraded by E3/3-macrophages to a greater extent than by E2/2-macrophages (2-fold), indicating that VLDL uptake is influenced by the phenotype of apoE secreted by macrophages. From these results, we conclude that both lipolysis by lipoprotein lipase and incorporation of apoE secreted from macrophages alter the affinity of VLDL for the LDL receptors on the cells, resulting in facilitation of their receptor-mediated endocytosis.

Modification of the T cell responsiveness to synthetic peptides by substituting amino acids on agretopes

T cell receptors, major histocompatibility complex molecules, and antigens constitute tri-molecular complexes which induce T cell activation. T cells in I-Ab mice generate proliferative responses to a synthetic peptide composed of residues 43-58 of pigeon cytochrome c (p43-58) and its analogs with substitution at position 50 (50A, 50V, 50L, 50N, 50Q, 50K, and 50M). However, none of these peptides stimulate T cells in I-Ak mice. We substituted two residues at positions 46 and 54 of p43-58(50D), 50V, 50L, 50E, and 50K with two amino acids on agretopes of the I-Ak binding HEL52-61 peptide and immunized I-Ak mice with these newly synthesized peptides: 46D50D54R, 46D50V54R, 46D50L54R, 46D50E54R, and 46D50K54R. Apart from 46D50D54R, these peptides elicited T cell responses in I-Ak mice in an immunogen-specific manner, but did not stimulate those in I-Ab mice. Further, 46D50V54R inhibited competitively the responses of I-Ak restricted T cell hybridomas specific for 46D50E54R. These results demonstrate that the residues at positions 46 and 54 on the peptides act as an agretope and the residue at position 50 acts as an epitope in I-Ak mice, as in I-Ab mice, and provide the possibility of opening up a new method to prepare peptide antigens which induce T cell responses in each murine strain by introducing appropriate amino acids on agretopes.

Plasma apolipoproteins in patients with multi-infarct dementia

We examined 27 elderly patients with multi-infarct dementia developed on the basis of cerebral arteriosclerosis. The levels of plasma cholesterol and triglyceride in the patients were 177 +/- 48 and 91 +/- 27 mg/dl (mean +/- SD), respectively. Despite normal plasma lipid levels, the patients had significantly higher plasma apo B (102 +/- 30 vs. 82 +/- 21 mg/dl for controls, P less than 0.01) and lower plasma apo A-I levels (104 +/- 25 vs. 130 +/- 22 mg/dl for controls, P less than 0.01) than the controls. Isoelectric focusing of apo E showed a 2-fold higher relative frequency for the epsilon 4 allele in patients than in Japanese controls (20.8 vs. 8.6-11.7% of total, P less than 0.05). The patients with phenotypes of E4/4 (n = 1) and E4/3 (n = 8) had higher plasma cholesterol levels than those with E3/3 (n = 15) (196 +/- 45 vs. 169 +/- 43 mg/dl). The results indicate that the patients had abnormalities in plasma lipoprotein metabolism and this may contribute to the development of cerebral arteriosclerosis.

Enhanced lipoprotein lipase secretion from human monocyte-derived macrophages caused by hypertriglyceridemic very low density lipoproteins

We studied the effects of very low density lipoprotein (VDL) obtained from hypertriglyceridemic subjects on the secretion of lipoprotein lipase and lipid accumulation in human monocyte-derived macrophages. The incubation of macrophages with VLDL obtained from different subjects caused different effects on the secretion of lipoprotein lipase (6.8 to 137.7 nM free fatty acid/min/mg cell protein) and triglyceride accumulation (184 to 507 micrograms/mg cell protein) in human monocyte-derived macrophages. VLDL from subjects with marked hypertriglyceridemia (approximately 1000 mg/dl) had a fourfold greater effect on lipoprotein lipase activity and a twofold greater effect on cellular triglyceride accumulation when compared with the effects of VLDL from normolipidemic subjects. Both lipoprotein lipase activity and triglyceride accumulation correlated positively with plasma VLDL triglyceride levels (r = 0.50 and 0.45, respectively, p less than 0.05). From these data, we suggest that the activity of lipoprotein lipase secreted from macrophages incubated with VLDL was dependent on triglyceride concentrations, and that the secretion of lipoprotein lipase enhanced by hypertriglyceridemic VLDL was closely related to the intracellular accumulation of triglyceride.

Strain differences in the early development of the thymus-dependent cells: precocity of T lineage cells in AKR mice as compared to those in C3H mice

Early development of T lineage cells were compared between AKR and C3H mice by using two experimental strategies--neonatal thymectomy (NTx) and bone marrow transplantation (BMT)--between these two strains of mice. After NTx, AKR mice developed less wasting disease and showed better maintenance of several T cell functions. In addition, the response of neonatal spleen cells to PHA and ConA was much greater in AKR mice than in C3H mice. Further, when AKR mice were used as recipients of BMT, cell numbers recovered from thymuses between 2 and 7 weeks after reconstitution were consistently much greater (about 10 times greater) than those from chimeras where C3H mice were used as recipients, regardless of the donor strains of bone marrow cells. However, 4 weeks after BMT the proliferative responses to ConA were consistently higher in the donor-derived thymocytes from chimeras where AKR mice were used as bone marrow donors than in those from chimeras in which C3H were donors. The present findings suggest that these differences may be attributed to characteristics of recipient microenvironment (e.g., thymic stroma) which maintain developing thymocytes and supply them to the peripheral lymphoid tissue. Alternatively the differences may to some degree also be attributable to characteristics of the thymic progenitors themselves, which may determine the rates of maturation of thymocyte functions.

A study on type II collagen-induced arthritis in allogeneic bone marrow chimaeras

In the present investigation, the incidence, day of onset and severity of type II collagen (IIC)-induced polyarthritis (CA) in allogeneic bone marrow chimaeras were compared. These chimaeras were prepared by using reciprocal combinations between DBA/1J (H-2q, Igh-1c, Hc1), which are highly susceptible to CA, and SWR/J (H-2q, Igh-1c, Hc0), which are CA resistant, strains of mice. The four kinds of chimaeras, [SWR----DBA/1], [DBA/1----DBA/1], [DBA/1----SWR] and [SWR----SWR], were shown to be full chimaeras. [SWR----DBA/1] and [DBA/1----DBA/1] chimaeras showed serum C5 antigens and most of these mice developed CA, even though severity of CA in [SWR----DBA/1] chimaeras was less than that in [DBA/1----DBA/1] syngeneic chimaeras. By contrast, [DBA/1----SWR] and [SWR----SWR] chimaeras completely lacked serum C5 and did not develop CA at all. However, most of these chimaeras produced considerable total IgG and IgG2a antibodies to IIC in the sera after immunization with the antigens, although differences in the serum levels of IgG2a antibodies were seen between [SWR----DBA/1] and [DBA/1----SWR] allogeneic chimaeras. The present results demonstrate directly a crucial role of complement cascade in the induction and development of CA and reveal that lymphoid cells of SWR mice potentially have the ability to develop CA. Differences in severity of the CA observed in some of these chimaeras, however, could not be readily explained by differences in C5 concentrations alone.

A study on graft-versus-host reaction (GVHR) by Simonsen's splenomegaly assay. Cells and antigen systems involved in induction of GVHR

Cells and histocompatibility antigen systems involved in graft-versus-host reactions (GVHR) were analyzed using Simonsen's splenomegaly assay employing various combinations of donor and F1 hybrid recipients mice. Most of the cells proliferating in spleens of mice undergoing GVHR were J11d+, and had histological features of cells of the hematopoietic lineage. The proportions of CD3+ T cells were decreased in the spleens. Disparity at minor histocompatibility determinants of AKR, I-E and H-2D regions between B10.A(4R) donors and (4R X AKR) F1 recipients evoked only negligible GVHR. On the contrary, disparity at H-2K and/or I-A regions appeared to be sufficient to permit induction of full GVHR. When surface markers of donor spleen cells were analyzed, it was shown that Thy-1+ and/or MEL-14+ cells caused a strong effect on GVHR. Further, either CD4+ or CD8+ T cell subset could induce significant GVHR. However, synergistic influences of these two T cell subsets on one another in GVHR were observed. The present results raise the possibility of using Simonsen's assay along with a number of reagents to identify the contribution of subsets of T lymphocytes and in analyzing precise contributions of cellular components from both donor and recipient, and also of the target antigen systems of the recipient that contribute to early events involved in GVHR.

Increased clearance of plasma cholesterol after injection of apolipoprotein E into Watanabe heritable hyperlipidemic rabbits

Apolipoprotein E (apoE) is known to play an important role in lipoprotein metabolism. We have studied the effect of apoE on the metabolism of plasma cholesterol by injecting apoE intravenously into rabbits deficient in low density lipoprotein receptors [Watanabe heritable hyperlipidemic (WHHL) rabbits]. Approximately 30 mg of apoE was injected per rabbit; a total of five WHHL rabbits were used. One hour later, plasma cholesterol levels fell 8.3% (from 488 +/- 192 to 446 +/- 174 mg/dl). After 3 hr, cholesterol levels had fallen by 19% (to 392 +/- 152 mg/dl). The reduced levels were maintained for at least 8 hr after injection of apoE. Cholesterol in very low density lipoproteins (VLDLs) and intermediate density lipoproteins fell rapidly during the first 2 hr after injection, followed by a reduction in the low density lipoprotein cholesterol level. Changes in apolipoprotein B levels in each lipoprotein fraction were very similar to those of cholesterol. Plasma apoE levels 3 min after injection were elevated 3-fold to 22.8 +/- 6.3 mg/dl and returned to initial levels 8 hr after injection. The rate of removal of intravenously injected 125I-labeled VLDL that had been incubated with apoE was 3-fold higher than that of unmodified VLDL. From these results, we conclude that the injected apoE is incorporated into VLDLs and that VLDL particles carrying more apoE are removed from the blood more rapidly, resulting in reduced formation of low density lipoprotein and lowered cholesterol levels.

Down-regulation of hepatic LDL receptor protein and messenger RNA in fasted rabbits

Rabbits fasted for 9 and 14 d exhibited 6- and 8-fold increase in plasma cholesterol level, respectively. As one of the mechanisms causing hypercholesterolemia in fasted rabbits, the decreased activity of hepatic low-density lipoproteins (LDL) receptor has been reported (Stoudemire, J.B., Renaud, G., Shames, D.M., & Havel, R.J. (1984) J. Lipid Res. 25, 33-39). In order to demonstrate the down-regulation of hepatic LDL receptor on a molecular basis, we carried out immunoblotting of the liver membranes with a specific antibody against LDL receptors and blot hybridization of hepatic RNAs with cDNA of LDL receptor. Immunoblotting showed that LDL receptors in fasted rabbits were markedly decreased, and blot hybridization of RNAs showed a significant decrease in mRNA level of hepatic LDL receptor in fasted rabbits. Further, significant decreases both in LDL binding to liver membrane and in hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in fasted rabbits were demonstrated. From these results, we concluded that hypercholesterolemia in fasted rabbits is caused by the impaired catabolism of LDL due to down-regulated biosynthesis of hepatic LDL receptor.

A case of acute diffuse lymphocytic meningoencephalitis

"Acute diffuse lymphocytic meningoencephalitis" is characterized neuropathologically by swelling of the brain and an unproportionally slight degree of inflammatory findings. Although many cases of this encephalitis have been reported in Japan, it was scarcely reported in other countries. The present case is a girl who had been well until fifteen years of age. She became psychotic on the 7th day after she seemed to have caught a cold. She fell into coma on the 15th day, then neurologic symptoms, such as nuchal rigidity and athetoid movement became prominent. She developed the status epilepticus with a high temperature of 41 degrees C, and died on the 23rd day. Although there was an increase of mononuclear cells in the cerebrospinal fluid (32/microliters), various antiviral titers were normal both in serum and cerebrospinal fluid. Neuropathologic changes were edema, perivascular lymphocytic infiltration in leptomeninges and parenchyma, and proliferation of rod-shaped microglia particularly prominent in the cerebral cortex and hippocampus. It is peculiar that thickening of leptomeninges formed by collagen fibers and inflammatory cells was observed. On the systemic study, centrolobular fatty change of the liver was found. This case had to be differentiated from several other neuro-psychiatric illnesses. The problems were discussed clinically and neuropathologically.