Normally, when a pathogen enters the body, an able immunity is capable of defeating most invasions. B-cells, T-cells, macrophages, neutrophils and others work in combination with one another to eliminate the threat and restore us back to health. It’s not always an easy process, however, and at times can lead to exhaustion. When this happens, our ability to fend off other invaders decreases. We essentially become more susceptible to other ailments.