Pattern recognition receptors (PRR) play an important roll in immediate responses to different conserved molecules produced by microbes. In this paper we describe the cloning of the mouse homolog of Toll-like receptor (TLR) 3, and present an analysis of the expression of this gene in innate and adaptive immune cell lines. We also performed a broad expression study on these cells of other TLR, including TLR family members whose expression pattern is not known, i.e. TLR7. The analysis was done in order to understand, and possibly predict, how innate and adaptive immune cells respond to microbial pattern antigens. This first large-scale analysis of immune cell TLR expression in the mouse reveals that cells of the innate immune system express a broader number of TLR than cells of the adaptive immune system, supporting preconceptions concerning the hierarchy of immune cells involved in direct pathogen recognition. Additionally, the expression of TLR transcripts by mast cells, neutrophils and microglial cells observed here suggests that pathogen-associated molecular pattern molecules could induce activation of these cells through TLR. Finally, the mouse homolog of human TLR3 identified here may, like its human counterpart, be an exceptional TLR molecule due to its lack of a conserved proline residue seen to be involved in existing TLR signaling capabilities found in other TLR family members.