Quercetin prevents UV-induced local immunosuppression, but does not affect UV-induced tumor growth in SKH-1 hairless mice.

Ultraviolet is thought to induce skin tumors by its dual activity as a mutagenic agent and a suppressor of cell-mediated immunity. In the present study the effects of quercetin, a flavonoid-containing compound, on carcinogenesis and immunosuppression were studied in SKH hairless mice exposed to suberythemal doses of UV for up to 17 weeks. It was found that quercetin did not affect the onset or growth of non-melanoma skin tumors resulting from UV exposure. In contrast, it prevented the suppression in contact hypersensitivity (CHS) to picryl chloride induced by UV. The mechanism of this prevention might be explained by the observation that the decreased number of epidermal Langerhans' cells is partly prevented by the quercetin. Quercetin did not alter the effects of UV in increasing numbers of spleen and lymph node cells, only partly in decreasing the CD8-positive cells in spleen cell populations and decreasing the lymphoproliferative response of spleen cells to the mitogens concanavalin A and phytohemagglutinin. Thus oral quercetin did not prevent UV-induced carcinogenesis although it restored the skin-associated CHS response probably by protecting the antigen-presenting cells in the skin.

Natural killer cell activity during UVR-induced skin tumor formation in the Skh hairless mouse.

We analyzed natural killer (NK) cell activity in the hairless albino Skh/HR1 mouse, to study whether the NK cell activity plays a role during UV radiation (UVR)-induced carcinogenesis. In 4 h 51Cr-release assays, spleen lymphocytes of specific pathogen-free (spf) Skh/HR1 mice displayed 5-10% spontaneous NK cell activity. This was comparable to NK cell activity in C57B1/6, C3H and athymic NMRI nu/nu mice, which were also kept under spf conditions. In all strains investigated, the low spontaneous NK cell activity could be increased up to 20-30% by intraperitoneal administration of polyinosinic:polycytidylic acid (polyI:C), a standardized in vivo NK cell induction method. The polyI:C potentiation of NK cells in Skh/HR1 mice was similar to that in C57B1/6 and NMRI, but significantly less than in C3H mice. Chronic daily UV irradiation according to a protocol that was also used for induction of carcinogenesis (11-12 weeks, 95 mJ/cm2 of UV exposure from FS40 sunlamps) did not decrease NK cell activity on a cell for cell basis. Neither was the inducibility of NK spleen cell activity with polyI:C in Skh/HR1 mice during UV exposure reduced. Based on total organ basis, the pooled lymph node cells (axillary, mandibulary and inguinal lymph node) showed a doubling of NK cell activity (P < 0.001), mainly due to an almost 100% increase in the number of lymph node cells. In conclusion, UVR does not suppress the normal or inducible NK cell activity at the time of clinical appearance of skin tumors. This suggests that such suppression of NK cell activity is not likely to contribute to UVR-induced carcinogenesis in the Skh/HR1 strain.

Induction of an antibody response in mice against human papillomavirus (HPV) type 16 after immunization with HPV recombinant Salmonella strains.

Human papillomaviruses (HPV) are present in approximately 95% of all cervical carcinomas and the HPV E6 and E7 genes are continuously expressed in these lesions. There is also circumstantial evidence that often natural immunity against HPV is generated and that this is of influence on HPV-induced lesions. Stimulation of the immune system by proper presentation of relevant HPV antigens might, therefore, lead to a prophylactic or therapeutic immunological intervention for HPV-induced lesions. For this purpose we have expressed the E6 and E7 protein of HPV 16 in an attenuated strain of Salmonella typhimurium (SL3261, aroA mutation), which has been used extensively as a live vector. Live recombinant Salmonella vaccines have the ability to elicit humoral, secretory and cell-mediated immune responses, including cytotoxic T cells, against the heterologous antigens they express. This report describes the construction of recombinant Salmonella strains expressing the HPV 16 E6 and E7 proteins, and the induction of an HPV-16-specific immune response in mice after immunization with these live vectors.

A helper T-cell epitope of the E7 protein of human papillomavirus type 16 in BALB/c mice.

The helper T-cell response to the E7 protein of human papillomavirus type 16 (HPV16) was studied using BALB/c (H-2d) mice. Twenty-two overlapping synthetic peptides spanning the HPV16 E7 protein were split into 6 groups. Mice were sensitized using mixtures of synthetic peptides corresponding to each of the groups. Lymph node cell suspensions were cultured with the corresponding mixture of synthetic peptides that was used for sensitization. Two mixtures induced a proliferative response. Analysis of the individual peptides from these mixtures showed that two (overlapping) peptides induced a proliferative response. This response was mediated by CD4+ cells. The common region of the two peptides was found to be a single epitope, and a minimal epitope was demonstrated (AHYNIVTFCCK). In conclusion, in contrast to others, we demonstrated a helper T-cell response in BALB/c mice. This may be due to the fact that we used synthetic peptides as immunizing agent. The helper T-cell epitopes in HPV16 E7 demonstrated previously are partly overlapping with the (minimal) epitope demonstrated here, underlining the 'public' nature of the epitope.