Immunologic and anti-immunosuppressive effects of vitamin A

Prenatally acquired vitamin A deficiency alters innate immune responses to human rotavirus in a gnotobiotic pig model

We examined how prenatally acquired vitamin A deficiency (VAD) modulates innate immune responses and human rotavirus (HRV) vaccine efficacy in a gnotobiotic (Gn) piglet model of HRV diarrhea. The VAD and vitamin A-sufficient (VAS) Gn pigs were vaccinated with attenuated HRV (AttHRV) with or without concurrent oral vitamin A supplementation (100,000 IU) and challenged with virulent HRV (VirHRV). Regardless of vaccination status, the numbers of conventional and plasmacytoid dendritic cells (cDCs and pDCs) were higher in VAD piglets prechallenge, but decreased substantially postchallenge as compared with VAS pigs. We observed significantly higher frequency of CD103 (integrin αEβ7) expressing DCs in VAS versus VAD piglets postchallenge, indicating that VAD may interfere with homing (including intestinal) phenotype acquisition. Post-VirHRV challenge, we observed longer and more pronounced diarrhea and higher VirHRV fecal titers in nonvaccinated VAD piglets. Consistent with higher VirHRV shedding titers, higher IFN-α levels were induced in control VAD versus VAS piglet sera at postchallenge day 2. Ex vivo HRV-stimulated mononuclear cells (MNCs) isolated from spleen and blood of VAD pigs prechallenge also produced more IFN-α. In contrast, at postchallenge day 10, we observed reduced IFN-α levels in VAD pigs that coincided with decreased TLR3(+) MNC frequencies. Numbers of necrotic MNCs were higher in VAD pigs in spleen (coincident with splenomegaly in other VAD animals) prechallenge and intestinal tissues (coincident with higher VirHRV induced intestinal damage) postchallenge. Thus, prenatal VAD caused an imbalance in innate immune responses and exacerbated VirHRV infection, whereas vitamin A supplementation failed to compensate for these VAD effects.

Improving medical approaches to primary CNS malignancies--retinoid therapy and more

Successfully inducing differentiation in ectodermal diseases, retinoids harbour considerable therapeutic potential in the treatment of neuroectodermal-neuroepithelial malignancies. The principal tissue retinoid, retinoic acid, can be potently upregulated in vivo by a relatively specific catabolic inhibitor, R75251 (liarozole). Both substances have been given orally over 2 years in addition to standard treatment, and have been well tolerated. Corresponding closely to plasma retinoid levels, cutaneous side effects facilitate individual dosing. We evaluate this adjuvant retinoid approach and additional efforts to improve therapy of primary CNS malignancies, including the topical administration of retinoids in gamma linolenic acid.

Adjuvant activity of all-trans-retinoic acid in C57Bl/6 mice

The effects of all-trans-retinoic acid were investigated on the immune responses in C57Bl/6 mice after daily oral administration for one week. In selected experiments the immunosuppressive chemicals, cyclophosphamide and cyclosporin A were used in conjunction with retinoic acid. Retinoic acid stimulated the production of antibodies against sheep red blood cells and DNP-Ficoll; however, retinoic acid did not reverse the depression caused by immunosuppressive chemicals. In non-immunized animals retinoic acid stimulated the production of IL-1 but not of IL-2. The mitogenic responses of splenocytes against concanavalin A, phytohemagglutinin and pokeweed mitogen were depressed after the retinoic acid treatment; those against lipopolysaccharide were not influenced. Treatment with retinoic acid did not alter the mixed leukocyte responses but increased the activity of NK cells. Results indicate that retinoic acid may act as an adjuvant via activating macrophages, however, retinoic acid cannot reverse the immunosuppression induced by potent chemicals.

Enhanced survival by vitamin A supplementation during a retrovirus infection causing murine AIDS

Infection by LP-BM5 murine leukemia virus (MuLV) produces an AIDS-like condition in mice. The viral infection suppressed the percentage of peripheral blood cells showing surface markers for macrophages, activated macrophages, T lymphocytes and activated lymphoid cells. High dietary vitamin A (retinyl palmitate) caused increased numbers of activated macrophages. It also increased the percentage of cells with markers for Ia+ cells and macrophages in the retrovirally infected mice compared to infected controls. In uninfected mice retinyl palmitate stimulated the percentage of cells with activated lymphocytes bearing IL-2R, and T cytotoxic cells. These were associated with a retarded death rate during infection with LP-BM5 murine leukemia in C57BL/6 mice. By 25 weeks of infection and 20 weeks of retinyl palmitate supplementation 71.3% survived, while 45.0% virally infected controls survived. The mice also had elevated numbers of B cells measured in the blood after 4 and 8 weeks of dietary treatment. Vitamin A stimulation may play a role in the slower death rate for retrovirally infected mice.

Immune function: relationship of nutrition and disease control. Vitamin A and beta-carotene on host defense

Even though the protective role played by vitamin A and beta-carotene against numerous diseases has been clearly demonstrated, the exact mechanism by which they afford this protection is not completely understood. Impairment of the animal's immune system resulting from the vitamin deficiency may account for increased susceptibility to infection. This article attempts to draw from available information on the effects of vitamin A and beta-carotene on specific and nonspecific host defense mechanisms as they relate to disease.

In vitro effects of retinoids on murine thymus-dependent and thymus-independent mitogenesis

The effects of three retinoids: all-trans-retinoic acid (RA), 13-cis-retinoic acid (13-cis-RA), and N-(4-hydroxyphenyl)retinamide (4-HPR) on murine splenic lymphocyte proliferative responses to mitogens were evaluated. The responses to T-cell mitogens, PHA and Con A, and a T-cell-dependent B-cell mitogen, PWM were significantly potentiated by these retinoids. However proliferative responses to a B-cell mitogen, Escherichia coli LPS were unaffected or inhibited. All three retinoids at concentrations ranging from 10(-6) to 10(-15) M significantly potentiated Con A-induced proliferative responses. In response to PWM, 10(-13) M RA, 10(-12) M 13-cis RA, and 10(-11) M 4-HPR were the lowest concentrations producing significant potentiation. Endpoint concentrations of retinoids significantly potentiating responses to PHA were; 10(-9) M RA, 10(-8) M 13-cis RA, and 10(-6) M 4-HPR. These responses were independent of retinol contained in fetal calf serum supplemented medium since responses were reproduced in serum-free medium devoid of retinol. Optimal potentiation by retinoids of responses to these T-cell-dependent mitogens were found at superoptimal concentrations of mitogen suggesting a selective inhibition of T-suppressor cells. Thus, potentiation of T-cell-dependent mitogen responses provides the most sensitive biological assay yet described for detection of retinoid activity and is a reproducible system to explore the cellular and molecular mechanisms of retinoid-mediated immunopotentiation.