Abstract: This invention is directed to a method for preparation of a biological sample for measurement of protein epitopes that allows for the preservation of intracellular protein epitopes and detection of signal transduction pathways based on the ability to capture transient activation states of the epitopes. The method provided by the invention allows for the rapid fixation of biological samples containing red blood cells, to ensure that epitopes of signal transduction molecules and other intracellular protein epitopes are preserved in the active state. The method of the invention further allows for lysis of red blood cells, thereby making it a useful method for cytometric analysis of biological samples, including, for example, whole blood, bone marrow aspirates, peritoneal fluids, and other red blood cell containing samples. The invention also provides a method to recover or “unmask” epitopes on intracellular antigens that have been made inaccessible by the cross linking fixative necessary to fix the sample.

Abstract: The present invention provides compositions and methods relating to avian leptin receptor binding domains. The present invention demonstrates that these compositions are useful for detecting the presence of leptin in a sample and distinguishing free leptin from bound leptin in multiple species. Methods and kits are presented for determining free leptin in a sample from an individual by assaying a sample for the binding of leptin to an avian leptin receptor binding domain, and detecting the bound leptin by using a labeled anti-leptin antibody.