In immunology, antibodies （immunoglobulins （Ig）） are classified into several types called isotypes or classes. The isotype of a primary antibody and the application it is being used in can result in background staining. Primary antibody background noise can be caused by binding to Fc receptors on target cells; by non-specific interactions with cellular proteins, carbohydrates, and lipids; or by cell autofluorescence. There are five antibody isotypes （IgA, IgD, IgE, IgG, and IgM） from mice, same as humans. Each isotype has a different heavy chain. Isotypes are also called classes. Another name for antibodies is immunoglobulin, hence the suffix of 'Ig' to designate antibody classes and subclasses. Naive B cells produce IgM and IgD. During B cell maturation, through isotypic switching, a mature B cell will produce one of IgG, or IgA, or IgE isotypes and subclasses. Different isotypes have different half-lives in vivo, ranging from 12 hours to 8 days.