Purpose: The role of macrophages in tumorigenesis is complex because they can both prevent and promote tumor development. Experimental Design: Four hundred forty-six colorectal cancer specimens were stained with the pan-monocyte/macrophage marker CD68, and average infiltration along the tumor front was semiquantitatively evaluated using a four-grade scale. Each section was similarly scored for the presence of CD68 hotspots. Some aspects of macrophage-tumor cell interactions were also studied using in vitro coculture systems. Results: Including all patients, regardless of surgical outcome and localization, survival increased incrementally with CD68TF Mean infiltration grade (P = 0.0001) but not in curatively resected colon cancers (P = 0.28). CD68 hotspot score (CD68TF Hotspot ) was divided into high and low. A high hotspot score conferred a highly significant survival advantage also in curatively resected colon cancer cases (n = 199, P = 0.0002) but not in rectal cancers. CD68TF Hotspot high turned out as an independent prognostic marker for colon cancer in multivariate analyses including gender, age, localization, grade, stage, tumor type, and lymphocytes at the tumor front, conferring a relative risk of 0.49 (P = 0.007). In vitro coculture experiments, using phorbol 12-myristate 13-acetate^activated U937 cells as macrophage model, revealed that a high ratio of macrophages to colon cancer cells inhibited cancer cell growth. This was partially dependent on cellto-cell contact, whereas Boyden chamber cocultivation without cell-to-cell contact promoted cancer cell spread. Conclusions: In conclusion, our data indicate that a dense macrophage infiltration at the tumor front positively influences prognosis in colon cancer and that the degree of cell-to-cell contact may influence the balance between protumorigenic and antitumorigenic properties of macrophages.

Bruton's tyrosine kinase (Btk) is thought to positively regulate mast cell activation, implying a role in allergic responses. We have compared acute and late phase allergic airway reactions in mice lacking either Btk or interleukin-2-inducible T cell kinase (Itk), another Tec kinase expressed in mast cells. Btk(-/-) mice showed minor protection against allergic symptoms when challenged with allergen via the airways. In sharp contrast, both acute and late phase inflammatory allergic responses were markedly reduced in Itk(-/-) mice. Notably, airway mast cell degranulation in Itk(-/-) mice was severely impaired, despite wild-type levels of allergen-specific IgE and IgG1. The degranulation defect was confirmed in DNP-conjugated human serum albumin-challenged mice passively sensitized with anti-DNP IgE antibodies, and was also observed after direct G-protein stimulation with the mast cell secretagogue c48/80. Moreover, late phase inflammatory changes, including eosinophilia, lymphocyte infiltration, and Th2 cytokine production in the lungs, was eliminated in Itk(-/-) mice. Collectively, our data suggest a critical role of Itk in airway mast cell degranulation in vivo that together with an impaired T cell response prevents the development of both acute and late phase inflammatory allergic reactions.