The Immaculate Conception is a doctrine of the Church. It says that Mary was conceived without Original sin, by a singular grace from God.
Where might we find support for this in the Bible? Luke 1:28, in the original Greek, for starters.
When the angel appeared to Mary, he addressed her as “full of grace” in the English translation. But this translation doesn’t do full justice to the full meaning of the text. In the ancient Greek (Koine Greek), the word used was “kecharitomene.” This word, used in the sentence in the manner in which it was, means that Mary was “full of grace” from the first moment of her existence (conception) and permanently thereafter. This means that she could not have had Original sin on her soul, because one cannot be “full” of grace and have any sin at the same time. Divine physics, if you will.