Systemic fungal infections occur when fungi enter the bloodstream and are able to cause more severe illnesses. They are often considered opportunistic infections, as they will arise within individuals with weakened immune systems. Unlike superficial fungal infections, they are often life-threatening. Prolonged neutropenia, a deficiency of white blood cells, following chemotherapy is a major risk factor for systemic fungal infections. The immune system is crucial to defending the body against systemic fungal infections.
The thymus plays a crucial role in the body’s defense by maturing the key agents of cell-mediated immunity. Cell mediated is a type of immune response which does not directly activate antibody production, but promotes cells which are able to engulf foreign agents. Cell-mediated immunity (CMI) is the main line of defense against systemic fungal infections. Th1-type CMI is necessary in order to clear fungal infections. Th1 type cells are a lineage of CD4+ effector T cells. They secrete chemical messengers known as cytokines which promote macrophage activation. Macrophages are known for their ability to engulf foreign invaders and subject them to lysis in their acidic sub-compartments.