What do you like doing in your spare time? http://xnxx.in.net/xnnx/ xnnx.com The scientists found that when Fel D1 comes in contact with a common bacteria toxin called lipopolysaccharide (LPS), it activates a receptor that recognizes the pathogen called Toll-like receptor 4 (TLR4). TLR4 is also the receptor that causes the allergic response to dust mites and the metal nickel. When TLR4 is turned on, it beefs up the body's immune system response to Fel D1. The response continues to grow, and the person's allergic symptoms become worse.