Harpins are glycine-rich and heat-stable proteins that are secreted through type III secretion system in gram-negative plant-pathogenic bacteria. Many studies show that these proteins are mostly targeted to the extracellular space of plant tissues, unlike bacterial effector proteins that act inside the plant cells. Over the two decades since the first harpin of pathogen origin, HrpN of Erwinia amylovora, was reported in 1992 as a cell-free elicitor of hypersensitive response (HR), diverse functional aspects of harpins have been determined. Some harpins were shown to have virulence activity, probably because of their involvement in the translocation of effector proteins into plant cytoplasm. Based on this function, harpins are now considered to be translocators. Their abilities of pore formation in the artificial membrane, binding to lipid components, and oligomerization are consistent with this idea. When harpins are applied to plants directly or expressed in plant cells, these proteins trigger diverse beneficial responses such as induction of defense responses against diverse pathogens and insects and enhancement of plant growth. Therefore, in this review, we will summarize the functions of harpins as virulence factors (or translocators) of bacterial pathogens, elicitors of HR and immune responses, and plant growth enhancers.

The molecular properties of immunosuppressive n-3 polyunsaturated fatty acids (PUFA) have not been fully elucidated. Using CD4⁺ T cells from wild-type control and fat-1 transgenic mice (enriched in n-3 PUFA), we show that membrane raft accumulation assessed by Laurdan (6-dodecanoyl-2-dimethyl aminonaphthalene) labeling was enhanced in fat-1 cells following immunological synapse (IS) formation by CD3-specific Ab expressing hybridoma cells. However, the localization of protein kinase Cθ, phospholipase Cγ-1, and F-actin into the IS was suppressed. In addition, both the phosphorylation status of phospholipase Cγ-1 at the IS and cell proliferation as assessed by CFSE labeling and [³H]thymidine incorporation were suppressed in fat-1 cells. These data imply that lipid rafts may be targets for the development of dietary agents for the treatment of autoimmune and chronic inflammatory diseases.

Bioactive food components containing n-3 polyunsaturated fatty acids (PUFA) modulate multiple determinants that link inflammation to cancer initiation and progression. Therefore, in this study, fat-1 transgenic mice, which convert endogenous n-6 PUFA to n-3 PUFA in multiple tissues, were injected with azoxymethane followed by three cycles of dextran sodium sulfate (DSS) to induce colitis-associated cancer. Fat-1 mice exhibited a reduced number of colonic adenocarcinomas per mouse (1.05 ± 0.29 versus 2.12 ± 0.51, P = 0.033), elevated apoptosis (P = 0.03), and a decrease in n-6 PUFA–derived eicosanoids, compared with wild-type (wt) mice. To determine whether the chemoprotective effects of n-3 PUFA could be attributed to its pleiotropic anti-inflammatory properties, colonic inflammation and injury scores were evaluated 5 days after DSS exposure followed by either a 3-day or 2-week recovery period. There was no effect of n-3 PUFA at 3 days. However, following a 2-week recovery period, colonic inflammation and ulceration scores returned to pretreatment levels compared with 3-day recovery only in fat-1 mice. For the purpose of examining the specific reactivity of lymphoid elements in the intestine, CD3⁺ T cells, CD4⁺ T helper cells, and macrophages from colonic lamina propria were quantified. Comparison of 3-day versus 2-week recovery time points revealed that fat-1 mice exhibited decreased (P < 0.05) CD3⁺, CD4⁺ T helper, and macrophage cell numbers per colon as compared with wt mice. These results suggest that the antitumorigenic effect of n-3 PUFA may be mediated, in part, via its anti-inflammatory properties. [Cancer Res 2008;68(10):3985–91]