Toll-like receptors and T-helper-1/T-helper-2 responses

Expression analysis of the Toll-like receptor and TIR domain adaptor families of zebrafish

The zebrafish genomic sequence database was analysed for the presence of genes encoding members of the Toll-like receptors (TLR) and interleukin receptors (IL-R) and associated adaptor proteins containing a TIR domain. The resulting predictions show the presence of one or more counterparts for the human TLR1, TLR2, TLR3, TLR4, TLR5, TLR7, TLR8, TLR9, IL-1R and IL-18R genes and one copy of the adaptor genes MyD88, MAL, TRIF and SARM. In contrast to data for the pufferfish Fugu rubripes, zebrafish has two genes that are highly similar to human TLR4. In addition, one fish-specific TLR group can be distinguished that is closely related to the Drosophila melanogaster Toll-9 gene. The sequence of cloned cDNAs for TLR4, TLR2 and MyD88 show the same intron-exon organisation as in the human counterparts. Expression analysis using reverse transcriptase-PCR (RT-PCR) shows that 17 of the predicted zebrafish TLR genes and all the genes encoding adaptor proteins are expressed in the adult stage. A subset of the TLR genes are expressed at higher levels in fish infected with the pathogen Mycobacterium marinum. The induced genes include the homologues of the human TLR1 and TLR2 genes, whose functions are associated with mycobacterial infections, underscoring the suitability of zebrafish as a model for analysis of the vertebrate innate immune system.

Toll receptors modulate allergic responses: interaction with dendritic cells, T cells and mast cells

PURPOSE OF REVIEW

The discovery of Toll-like receptors has generated much interest in understanding the impact of innate immunity on adaptive immune responses, including allergic diseases.

RECENT FINDINGS

Recent studies suggest that Toll-like receptor pathways may mediate interactions between dendritic cells, T lymphocytes and mast cells, thus modulating allergic immune responses. Toll-like receptor signaling triggers dendritic cell maturation, which primes naive T lymphocytes towards specific T helper cell types 1 and 2 immune responses. Although a T helper cell type 1/2 balance may be important in modulating allergic responses, T regulatory cells that suppress certain immune responses may be critical in immune regulation.

SUMMARY

With the identification of different subsets of dendritic cells and the discovery of Toll-like receptors on T regulatory cells and mast cells, the manipulation of Toll-like receptor signaling may lead to novel therapeutic options in allergic diseases.