Expression of lymphocyte-specific chemokines in human malignant glioma: Essential role of LARC in cellular immunity of malignant glioma

Lymphocytes are frequently observed in human malignant glioma, the mechanism(s) underlying their appearance is not fully understood. To clarify tumor immunity in malignant gliomas, we analyzed the expression of 8 novel lymphocyte-specific chemokines in human glioma cell lines and glioma tissues by RT-PCR, Northern blot, immunoblot and immunohistochemistry, and examined the correlation with the infiltration of various subsets of lymphocytes. For the 8 chemokines examined (LARC, TARC, ELC, SLC, PARC, LEC, HCC-2, and SCM-1α), expression of LARC was clearly detectable in all 12 glioma cell lines by RT-PCR. Additionally, expression of TARC and SCM-1α was detectable in the majority of glioma cell lines. However, the expression level of most chemokines was low, so that Northern blot analysis could not demonstrate their expression with the exception of LARC in 2 cell lines. Expression of LARC mRNA and LARC protein was strongly induced by phorbol myristate ester in U87 MG cells. The production of LARC protein was demonstrated in 4 of 8 glioblastoma tissues by immunoblotting, and 9 of 33 samples (27.3%) by immunohistochemistry. Interestingly, the positivity of LARC staining was significantly correlated with the infiltration of CD8-, CD4-, and CD45R0-positive cells (p<0.001). Although the constitutive expression level of LARC is low, certain stimulations could strongly induce its expression, and play a crucial role in the tumor immunity of human malignant glioma.