Histamine metabolism in skin of MRL/l mice

Lupus gut microbiota transplants cause autoimmunity and inflammation

BACKGROUND

The etiology of systemic lupus erythematosus (SLE) is multifactorial. Recently, growing evidence suggests that the microbiota plays a role in SLE, yet whether gut microbiota participates in the development of SLE remains largely unknown. To investigate this issue, we carried out 16 s rDNA sequencing analyses in a cohort of 18 female un-treated active SLE patients and 7 female healthy controls, and performed fecal microbiota transplantation from patients and healthy controls to germ-free (GF) mice.

RESULTS

Compared to the healthy controls, we found no significant different microbial diversity but some significantly different species in SLE patients including Turicibacter genus and other 5 species. Fecal transfer from SLE patients to GF mice caused GF mice to develop a series of lupus-like phenotypic features, including increased serum autoimmune antibodies, imbalanced cytokines, altered distribution of immune cells in mucosal and peripheral immune response, and upregulated expression of genes related to SLE in recipient mice that received SLE fecal microbiota transplantation (FMT). Moreover, the metabolism of histidine was significantly altered in GF mice treated with SLE patient feces, as compared to those which received healthy fecal transplants.

CONCLUSIONS

Overall, our results describe a causal role of aberrant gut microbiota in contributing to the pathogenesis of SLE. The interplay of gut microbial and histidine metabolism may be one of the mechanisms intertwined with autoimmune activation in SLE.

Severer lupus erythematosus-like skin lesions in MRL/lpr mice with homozygous Kitwsh/wsh mutation

OBJECTIVE

To clarify the roles of mast cells (MCs) on the pathogenesis of lupus erythematosus (LE)-like skin lesions on MRL/lpr mice.

METHODS

MRL/lpr mice were mated with C57BL/6-Kit^wsh/wsh mice and the heterozygous F1 mice were 10 times backcrossed with the parental MRL/lpr to generate MRL/lpr-Kit^wsh/wsh mice. MC-deficient MRL/lpr-Kit^wsh/wsh mice were compared with MRL/lpr-Kit^+/+ and MRL/lpr-Kit^wsh/+ mice with intact MCs.

RESULTS

MRL/lpr-Kit^wsh/wsh mice developed skin lesions without infiltrating MCs. As similar skin lesions on MRL/lpr-Kit^+/+ mice and MRL/lpr-Kit^wsh/+ mice contain comparable number of MCs, these mice were collectively analyzed as MRL/lpr mice with MCs. Compared with MRL/lpr mice with MCs, skin lesions developed earlier and showed consistently higher severity, with significantly higher mRNA expressions of many inflammatory cytokines in the dorsal skin on MRL/lpr mice without MCs. Furthermore, survival rate was significantly lower in MRL/lpr mice without MCs. The number of infiltrating MCs significantly increased in association with the severity of skin lesions in MRL/lpr mice with MCs.

CONCLUSIONS

These results demonstrated that MCs are infiltrated to suppress the progression of LE-like skin lesions in MRL/lpr mice.

The protective effects of ultraviolet A1 irradiation on spontaneous lupus erythematosus-like skin lesions in MRL/lpr mice

We investigated the effects of ultraviolet A1 (UVA1) irradiation on spontaneous lupus erythematosus- (LE-) like skin lesions of MRL/lpr mice, using a disease prevention model. UVA1 irradiation significantly inhibited the development of LE-like skin lesions, without obvious changes of the disease including renal disease and serum antinuclear antibody levels. Besides the massive infiltration of mast cells in the LE-like skin lesions, in the nonlesional skins, more mast cells infiltrated in the UVA1-irradiated group compared with the nonirradiated group. Although apoptotic cells were remarkably seen in the dermis of UVA1-irradiated mice, those cells were hardly detectable in the dermis of the nonirradiated mice without skin lesions. Further analysis showed that some of those apoptotic cells were mast cells. Thus, UVA1 might exert its effects, at least in part, through the induction of the apoptosis of pathogenic mast cells. Our results supported the clinical efficacy of UVA1 irradiation for skin lesions of lupus patients.

Mast cells and histamine metabolism in skin lesions from MRL/MP-lpr/lpr mice

It is likely that mast cell and histamine metabolism are involved in autoimmune tissue injury such as cutaneous lupus erythematosus (LE) because different histamine receptors can regulate Th1 and Th2 cells. In order to verify the role of the axis of mast cell-histamine metabolism-histamine receptor, the autoimmune mouse has been investigated. The MRL/Mp-lpr/lpr (MRL/lpr) mouse is a good model for the spontaneous development of skin lesions similar to those seen in human LE. In skin lesions from MRL/l mice, there are many infiltrating T cells and mast cells in the dermis and impaired histamine metabolism, in which the low activity of histamine-N-methyltransferase and the related prolonged effects of histamine in the skin tissue seem to play a definite pathological role in the development of spontaneous lupus-like eruptions. The expression of H2R on the mast cell decreases within these skin lesions at 5 months of age. It is interesting that the activity of HMT runs in parallel with the expression of H2R over the time course of the skin changes in MRL/l mice, but the relationship between these two observations remains obscure. The accumulation of mast cells expressing H2R and prolonged effects of histamine may occur to regulate the production of Th1 and Th2 cytokines in the skin lesions of MRL/l mice.

FK506: therapeutic effects on lupus dermatoses in autoimmune-prone MRL/Mp-lpr/lpr mice

The effects of FK506, a new immunosuppressive agent, on the development of lupus dermatoses were investigated in the autoimmune-prone MRL/Mp-lpr/lpr (MRL/lpr) mouse, which is an animal model for the spontaneous development of skin lesions similar to those of human lupus erythematosus (LE). FK506 reduced the incidence of skin lesions, lupus nephritis, the titre of serum anti-double-stranded DNA antibodies and the massive T cell proliferation. The incidence and magnitude of IgG deposition at the dermoepidermal junction were not changed. These results suggest that FK506 is a promising immunosuppressive agent for the control of autoimmune skin diseases.

Histamine metabolism in delayed type hypersensitivity--comparative analysis with cellular infiltrates

We examined the dynamic changes of histamine metabolism and infiltrating cell populations in lesional sites of representative cutaneous delayed type hypersensitivity (DTH), including dinitrochlorobenzene (DNCB) allergic dermatitis, purified protein derivative of tuberculin (PPD) reaction, and keyhole limpet homocyanin (KLH)-induced cutaneous basophil hypersensitivity. The concentration of histamine increased with time in all DTH reactions examined, though the time course varied among these reactions. In DNCB allergic dermatitis, the maximum content of the amine at 3 days after the initiation was about three times that of the control baseline. In PPD reaction, the maximum content and the time course were almost similar to that in DNCB allergic dermatitis. However, in KLH-induced cutaneous basophil hypersensitivity the maximum content was about ten times that in DNCB allergic dermatitis or PPD reaction, and was observed earlier, on the 2nd day. There was no remarkable change in the activities of histamine-degrading enzymes in these reactions. There was little infiltration of mast cells, while time-dependent changes of the basophil infiltration were almost parallel those of the histamine concentration in all these reactions. Basophils in DNCB allergic dermatitis showed a piecemeal degranulation, while those in either the PPD reaction or KLH-induced cutaneous basophil hypersensitivity remained intact. These results clearly suggest that the increase of histamine concentration in cutaneous DTH depends on the number of basophils infiltrating the lesional sites, even if the regulatory mechanisms of the activation of the cells differ among the DTH reactions.

Biogenic amines in the Arthus reaction

The concentrations of serotonin, tryptamine, dopamine, and tyramine were quantitatively determined in the Arthus reaction, since the activity of histamine-N-methyltransferase (HMT), a major histamine-metabolizing enzyme that had been demonstrated to be inhibited by such biogenic amines in vitro, decreased significantly in the reaction site. The concentrations of serotonin, tryptamine, and dopamine were unchanged in dinitrochlorobenzene allergic and croton oil dermatitis except for a slight increase of tryptamine in the latter. Tyramine was unable to be demonstrated quantitatively in all specimens tested. The concentration of serotonin decreased to about 30% that of the control level until 1 hr, followed by a prominent increase to about two-fold at 6 hr after the initiation of the Arthus reaction accompanying with a concomitant decrease in HMT activity. However, the concentrations of tryptamine and dopamine were rather decreased in the reaction site, and the net decrease of two amines was far greater than the increased amount of serotonin. The decrease in HMT activity is not stoichiometrically well elucidated from these results, and therefore, the presence of other hypothetic inhibitory factors that are increased in the Arthus reaction should be suspected.

Regulation of the activity of histamine-N-methyltransferase from guinea pig skin by biogenic amines

Histamine-N-methyltransferase, a major histamine-degrading enzyme in the skin, was purified from guinea pig skin about 150-fold. The enzymological characteristics including pH optimum, Km values for substrates, and molecular weight were almost consistent with those reported in the brain. Regulatory mechanism of the enzyme activity by biogenic amines was investigated using the purified specimen. Serotonin, tryptamine, and 5-methoxytryptamine intensely inhibited the activity while tryptophan, melatonin, N-acetylserotonin, tryptophol, and 5-hydroxyindole acetic acid had no significant effects. Dopamine, tyramine, 3-methyltyramine, and phenylethylamine also inhibited the activity while no particular effects were obtained by adrenaline, noradrenaline, tyrosine, and DOPA. Spermidine and cadaverine caused significant but weaker inhibition. These amines acted competitively with respect to histamine, although varying manners were observed with respect to S-adenosyl-L-methionine. From these results, it was concluded that the enzyme activity was inhibited by such compounds in which a certain chemical structure, CH2-CH2-NH2 group neighboring the hydrophobic group, was contained. A possible mechanism of inhibition by the amines is postulated, and possible roles of such compounds in the inflammation by impairing the histamine metabolism is discussed.

Ultrastructural lupus band test in the skin of MRL mice

The ultrastructural localization of immunoglobulin deposits in the dermoepidermal junction of MRL/l mice was examined using immunoperoxidase staining. All specimens that showed positive findings at the basement membrane zone of the skin on light microscopy had reaction products at the sub-basal laminar area when observed by electron microscopy. In the skin that had no distinct eruptions or which was distant from the lesions, the reaction products were distributed mostly just beneath the basal lamina in fine to course granular deposits. In the lesional skin, they formed a rather uniformly granular pattern among the irregularly arranged collagen fibrils and increased fine fibrillar amorphous material under the highly infolded basal lamina. Some of the reaction products were located just on the collagen fibrils and some appeared to be related to the free basal lamina. From the perspective of immunoelectron microscopy, the skin eruptions of MRL/l mice may serve as a good dermatological model of human systemic lupus erythematosus.

Histamine metabolism in the Arthus reaction

Histamine metabolism, i.e., concentration of histamine and activities of histamine-degrading enzymes, histamine-N-methyltransferase (HMT), and diamine oxidase (DAO), were examined in the Arthus reaction induced in guinea pig skin. The specific activity of HMT was 44.12 +/- 3.80 pmole/min/mg protein and was about 15 times greater than that of DAO in control specimens. However, HMT activity decreased time dependently to 35% of the control at 3 hr and to 10% 48 hr after the initiation of the reaction. DAO activity increased to 150% till 1 hr followed by a linear decrease to 35% at 6 hr and to 10% at 48 hr. Histamine concentration showed a prominent linear decrease to 15% of the control at 2 hr followed by an increase to about 85% at 6 hr. This biphasic change seemed to be well explained by the dynamic changes in the activities of histamine-degrading enzymes. Such decrease in enzyme activities were not observed in other experimentally induced inflammations including dinitrochlorobenzene allergic and croton oil dermatitis. The addition of tissue extract from the Arthus reaction sites resulted in about 30% inhibition in both of two enzyme activities, suggesting the presence of some inhibitory factor(s) in the reaction sites.