Why is $DPT$ called a Triple antigen?

(N/A) $DPT$ is known as a Triple antigen because it is a vaccine that provides immunity against three distinct diseases:
$(i)$ Diphtheria: Caused by the bacterium $Corynebacterium$ $\text{diphtheriae}$.
$(ii)$ Pertussis: Also known as whooping cough, caused by the bacterium $Bordetella$ $\text{pertussis}$.
$(iii)$ Tetanus: Caused by the bacterium $Clostridium$ $\text{tetani}$.
Since it protects against these three specific pathogens simultaneously, it is referred to as a Triple antigen.