IgE production after antigen-specific and cognate activation of HLA-DPw4-restricted T-cell clones, by 78% of randomly selected B-cell donors

Assessing the function of human UNC-93B in Toll-like receptor signaling and major histocompatibility complex II response

The high sequence identity observed between UNC-93B of mouse and human imply common evolutionary ancestors and a conserved function. A nonconservative point mutation in the mouse Unc93b1 gene has been associated with defective Toll-like receptor (TLR) signaling and impaired major histocompatibility complex (MHC) I and II restricted antigen responses. Like murine UNC-93B, the human homologue is predicted to form 12 transmembrane domains, and it localizes to the endoplasmic reticulum. In human beings its expression is highest in professional antigen-presenting cells such as dendritic cells and macrophages. Interestingly, UNC-93B itself is specifically induced by TLR3 signaling in monocyte-derived dendritic cells and macrophages. To study the effect of UNC-93B deficiency in TLR signaling and antigen-presentation in human beings, UNC-93B message was knocked down in monocyte-derived dendritic cells and a reduced TNFalpha production in response to TLR3 agonists was observed. In the same experiment, the achieved knockdown had no effect on an MHC II-dependent antigen response, suggesting that the reduced quantity of human UNC-93B was still capable of supporting class II antigen presentation or that UNC-93B is not required for class II antigen presentation in human antigen-presenting cells.

EWI-2/CD316 is an inducible receptor of HSPA8 on human dendritic cells

The activation of dendritic cells is marked by changes both on their cell surfaces and in their functions. We define EWI-2/CD316 as an early activation marker of dendritic cells upregulated by Toll-like receptor ligands clearly before CD86 and CD83. By expression cloning, human heat shock protein A8 (HSPA8), a member of the hsp70 family, was identified as the ligand for EWI-2. Soluble EWI-2 bound both to cells expressing HSPA8 and also to immobilized HSPA8 protein. Although heat shock proteins are evolutionarily well conserved, other members of this class, including human hsp60 and mycobacterial hsp65, did not bind to EWI-2. The ligation of EWI-2 enhanced the CCL21/SLC-dependent migration of activated mature dendritic cells but attenuated their antigen-specific stimulatory capacities. Important functions of recently activated dendritic cells are thus critically modulated by the newly discovered HSPA8-EWI-2 interaction.

Identification of a common HLA-DP4-restricted T-cell epitope in the conserved region of the respiratory syncytial virus G protein

The cellular immune response to respiratory syncytial virus (RSV) is important in both protection and immunopathogenesis. In contrast to HLA class I, HLA class II-restricted RSV-specific T-cell epitopes have not been identified. Here, we describe the generation and characterization of two human RSV-specific CD4(+)-T-cell clones (TCCs) associated with type 0-like cytokine profiles. TCC 1 was specific for the matrix protein and restricted over HLA-DPB1*1601, while TCC 2 was specific for the attachment protein G and restricted over either HLA-DPB1*0401 or -0402. Interestingly, the latter epitope is conserved in both RSV type A and B viruses. Given the high allele frequencies of HLA-DPB1*0401 and -0402 worldwide, this epitope could be widely recognized and boosted by recurrent RSV infections. Indeed, peptide stimulation of peripheral blood mononuclear cells from healthy adults resulted in the detection of specific responses in 8 of 13 donors. Additional G-specific TCCs were generated from three of these cultures, which recognized the identical (n = 2) or almost identical (n = 1) HLA-DP4-restricted epitope as TCC 2. No significant differences were found between the capacities of cell lines obtained from infants with severe (n = 41) or mild (n = 46) RSV lower respiratory tract infections to function as antigen-presenting cells to the G-specific TCCs, suggesting that the severity of RSV disease is not linked to the allelic frequency of HLA-DP4. In conclusion, we have identified an RSV G-specific human T helper cell epitope restricted by the widely expressed HLA class II alleles DPB1*0401 and -0402. Its putative role in protection and/or immunopathogenesis remains to be determined.