The immune system starts to develop in the fetus, and it is a dynamic organ active throughout life with many different types of cells and many different cellular functions. Persons with Bloom's syndrome have an immune system and are able to produce antibodies in response to infections. The immune system contains all the different types of cells with the various cellular functions that are present in normal persons; however, the Bloom's immune system is weak in its ability to fight off infections. It lacks the full range of cellular responses and it lacks the usual complement of immune globulins (proteins that constitute the antibodies). When immune cells are called to fight infections, there is a stage in which the cells divide and proliferate. Could the inability to fight off infections normally be related to the problems Bloom's cells encounter when trying to divide and proliferate? Could the hematopoietic stem cells* have trouble keeping up with the proliferation needs demanded by infections?
*For more information about stem cells, please see Small Body Size.