So let's begin by defining and discussing what a primary response is. So the first time that our body is ever invaded by some particular pathogen that carries its own antigen, our body, our immune system, responds in a certain way. And this response we call the primary response. So let's suppose our pathogen makes its way into our tissues and releases its pathogenic antigen. Now, at this particular moment in time, we have never actually seen our immune system has never actually seen this particular antigen. And what that means is we're going to have no corresponding antibodies in our body, in our blood, that can actually bind to that particular antigen.