When a disease-causing agent enters an organism the immune system alerts which specialized cells?

When a disease-causing agent enters an organism, the immune system primarily alerts specialized cells called macrophages and dendritic cells. These antigen-presenting cells recognize and engulf the pathogens, processing their antigens and presenting them to T cells. This activation leads to a coordinated immune response involving various other immune cells, including B cells and helper T cells, to effectively target and eliminate the threat.