The mechanism of CD8 cooperation with the TCR in antigen recognition was studied on live T cells. Fluorescence correlation measurements yielded evidence of the presence of two TCR and CD8 subpopulations with different lateral diffusion rate constants. Independently, evidence for two subpopulations was derived from the experimentally observed two distinct association phases of cognate peptide bound to class I MHC (pMHC) tetramers and the T cells. The fast phase rate constant ((1.7 +/- 0.2) x 10(5) M(-1) s(-1)) was independent of examined cell type or MHC-bound peptides' structure. Its value was much faster than that of the association of soluble pMHC and TCR ((7.0 +/- 0.3) x 10(3) M(-1) s(-1)), and close to that of the association of soluble pMHC with CD8 ((1-2) x 10(5) M(-1) s(-1)). The fast binding phase disappeared when CD8-pMHC interaction was blocked by a CD8-specific mAb. The latter rate constant was slowed down approximately 10-fold after cells treatment with methyl-beta-cyclodextrin. These results suggest that the most efficient pMHC-cell association route corresponds to a fast tetramer binding to a colocalized CD8-TCR subpopulation, which apparently resides within membrane rafts: the reaction starts by pMHC association with the CD8. This markedly faster step significantly increases the probability of pMHC-TCR encounters and thereby promotes pMHC association with CD8-proximal TCR. The slow binding phase is assigned to pMHC association with a noncolocalized CD8-TCR subpopulation. Taken together with results of cytotoxicity assays, our data suggest that the colocalized, raft-associated CD8-TCR subpopulation is the one capable of inducing T-cell activation.
Interleukin (IL)-32 is a recently identified proinflammatory cytokine that is one of the IL-18 inducible genes, and plays an important role in autoimmune and inflammatory diseases. We produced antibodies against IL-32 and studied the expression of IL-32 in human stomach cancer. We detected IL-32 secreted from K-562 cells that werw stably transfected with IL-32 and in the sera of stomach cancer patients, by a sandwich ELISA using a monoclonal antibody KU32-52 and a polyclonal antibody. In order to optimize a sandwich immunoassay, recombinant IL-32alpha was added, followed by the addition of a biotinylated KU32-52 into microtiter plate wells precoated with a goat anti-IL-32 antibody. The bound biotinylated KU32-52 was probed with a streptavidin conjugated to HRP. This sandwich ELISA was highly specific and had a minimal detection limit of 80 pg/ml (mean+/-SD of zero calibrator) and measuring up to 3,000 pg/ml. This ELISA showed no cross-reaction with other cytokines such as hIL-1alpha, hIL-1beta, hIL-2, hIL-6, hIL-8, hIL-10, hIL-18, and hTNF-alpha. Intra-assay coefficients of variation were 18.5% to 4.6% (n=10), and inter-assay coefficients were 23% to 9% (n=10). The average IL-32 level in the sera of 16 stomach cancer patients (189 pg/ml) was higher than that of 12 healthy control men (109 pg/ml). Our results indicate that serum IL-32 level can be detected by using an established ELISA, and that this immunoassay and mAb KU32-09 specific for immunohistochemistry can be used in the detection of expressed and secreted IL- 32 in stomach cancer patients.
