Early HIV symptoms

Hi,

I wanted to know why is it that some people show early symptoms of HIV and some others dont. Does it have to do with the immunity of each individual? Am I right in guessing that those with a stronger immune system are able to tackle the early effects of the virus? Amongst those who show early symptoms, does the severity of the flu/lymph node enlargement/body aches also vary? Or does everyone show fairly strong symptoms?

Thanks.