I stained mouse lymph nodes with pd-1,cxcr5,cd4 and cd44 for t follicular helper cells and cd19,cd38,cd73 and af488 conjugated to an antigen that I originally immunized the mice with. I collected the samples at day0, day5 and day42. My mice were 6 weeks old at the time of immunization, is it typical to not see much staining for pd-1? And I also did not see many cells staining for cd73 at day 42. How long does it typically take for memory b cells to develop?