Induction of CD4+ regulatory T cells by TPA in mice: contra-suppression by CD8+ T cells

Dose dependence of oral tolerance to nickel

The dose dependence of oral nickel tolerance was analyzed by comparing three different subsets of C57BL/6 mice: Ni(very low) mice were reared in a nickel-reduced environment, Ni(low) and Ni(high) mice were reared in a stainless steel-containing environment and the latter received oral NiCl(2) (10 mM). In spleen and feces, Ni(very low) mice exhibit significantly lower nickel concentrations than Ni(low) and Ni(high) mice. In contrast to Ni(very low) mice that can be sensitized with a single intradermal administration of NiCl(2) alone, Ni(low) mice can only be sensitized in the presence of an adjuvant and Ni(high) mice cannot be sensitized at all. This dose-dependent resistance to nickel sensitization (i.e. Ni(high) > Ni(low) > Ni(very low)) correlates with differences in the number and type of nickel-specific T regulatory (Treg) cells. Adoptive transfer studies into Ni(very low) recipients showed that Ni(very low) mice completely lack specific Treg cells whereas Ni(low) and Ni(high) mice harbor them, albeit their numbers and/or suppressive strength are much higher in Ni(high) than Ni(low) mice. The principal Treg subset in Ni(low) mice consists of CD4(+)CD25(+) cells, among which CD4(+)CD25(+)alpha(E)beta(7)(+) cells are the most effective. In Ni(high) mice, CD4(+)CD25(+) Treg cells co-exist with an ensemble of CD8(+) Treg and CD4(+)CD25(-) suppressor-inducer cells.

Evolution of the thymus size in response to physiological and random events throughout life

During embryogenesis and in the early stages of life, the thymus is a crucial organ for the generation of the T cell repertoire. T cells are generated from hematopoietic stem cells already differentiated to precursor T cells in the bone marrow. These cells enter the thymus guided by chemotactic factors secreted by this organ. The complex maturation process takes place that ensures self-tolerance and homeostasis. Thymocytes that show autoreactivity do not leave the thymus, but rather die by apoptosis. The final percentage of mature T cells that survive to migrate from the thymus to the periphery is very low: at most 5%, under optimal conditions. The highest migration occurs in childhood and adulthood, at least in mice and humans; however, it declines throughout life and is minimal in the elderly. Under normal circumstances, the thymus commences involution soon after birth, and this involution correlates with the capacity to export mature T cells to the periphery. Hormones, cytokines, and neurotransmitters all play a role in this age-associated process, but the reasons for and mechanisms of this involution remain unknown. Apart from physiological conditions that change throughout life and govern age-related thymus evolution, random states and events provoked by intrinsic or extrinsic factors can induce either thymus involution, as in reversible transient thymic hypoplasias, or thymic hyperplasias. The age-associated involution, unlike transient involutions, follows a regular pattern for all individuals, though there are clear differences between the sexes. Nevertheless, even the age-associated involution seems to be reversible, raising the possibility of therapeutic strategies aimed at enhancing thymus function in the elderly.

[Microanalysis of tryptophan metabolites and suppressor factor of delayed-type hypersensitivity in mice]

We developed methods for the fluorometric assay of 3-hydroxykynurenine and 3-hydroxy-anthranilic acid, which are suspected as carcinogens in bladder cancer. It was shown that the urinary excretion of 3-hydroxyanthranilic acid increased in patients with bladder cancer. We also developed methods for the fluorometric assay of glucuronide and sulfate of 3-hydroxyanthranilic acid and showed that the excretion of these conjugated forms was minor in humans. The distribution of 3-hydroxykynurenine was studied and data obtained suggested that it has an affinity for the pancreas. We then developed methods for determination of the related compounds of tryptophan. Fluorescence reaction with UV radiation was applied to the determinations of kynurenic acid, kynurenine, quinolinic acid, nicotinic acid, nicotinamide, N1-methyl-nicotinamide, isatin, xanthrenic acid, and melatonin in the serum or urine. Furthermore, the fluorescence reaction with UV radiation was applied to some drugs, e.g., indomethacin, isoniazid, naldixic acid, nicorandil, and disodium cromoglycate. The relationship was investigated between the tumor promoter, 12-tetradecanoyl-phobol-13-acetate (TPA), and delayed hypersensitivity in mice. The foot pad reaction (FPR) in mice was suppressed by the application of TPA following the application of 7,12-dimethylbenz[alpha]-anthracene (DMBA), a tumor initiator, in BALB/c mice, while the FPR was suppressed by the application of TPA alone in C3H/He mice. CD8+ and CD4+ T cells, which suppress the FPR, were induced in BALB/c and C3H/He mice, respectively. These T cells produced soluble factors that inhibited the FPR in mice.