The clone recognizes a 170-180 kD alpha chain of a type I transmembrane glycoprotein also known as CD11a or LFA-1a. It is also known as LFA-1a. CD11a non-covalently associates with integrin ß2 (CD18) to form LFA-1. CD11a is abundantly expressed on all leukocytes, including B and T lymphocytes, monocytes, macrophages, neutrophils, basophils and eosinophils but does not express by the non-hematopoietic tissues and platelets. Up-regulation of CD11a on activated lymphocytes is required to induce their immune response. Absence or reduced CD11a expression on tumor cells helps to escape from regular immune surveillance and it may be one of reason of in vivo tumor generation.