What is the highest post-doctoral salary one should ask for (immunology)
Postdoc salaries as high as 60K are not unheard of, especially if the cost of living is high and/or you have children. I believe some very competitive "independent postdoc" positions can even reach as high as 70K. However, these salaries may not increase annually, while typically lower salaries do increase annually.

BTW I believe the average 1st year postdoc salary is under 40K (and so is the NIH postdoc salary guideline).