The immune system responds to bacterial infections in two major ways. First, it may respond to soluble products of the cell such as toxins or released structural antigens like LPS of a given gram-negative bacterial cell. Most bacterial antigens are T cell dependent and require helper T cells for initiation of the immune response. Yet certain cell antigens, such as the pneumococcal polysaccharides, are T cell independent. They are large-molecule-weight molecules, and in children, antibody response to these antigens may take four to six years. Thus, younger children are susceptible to these infections.