Investigating heterogeneity within T follicular helper cells (TFH) population.

T follicular helper cells (TFH) are heterogenic population of CD4+ T cells, expressing CXCR5+ and PD-1+ on their surface. Their role is linked to supporting formation of germinal centres (GC) and these cells are thought to express high levels of PD-1 marker. Two models of immunisation were used to investigate the role of PD-1 low TFH. In Salmonella enterica infection high frequency of T follicular helper cells expressing low levels of PD-1 surface molecule are observed within first week of infection but GC do not appear until much a later stage (week 7-8). Sheep red blood cell immunisation (SRBC) gives rise to both TFH and GC B cells within first week of response and these TFH express low to high level of PD-1 molecule. Microarray analysis was applied in order to investigate the relationship between and characteristics of different TFH populations in order to elucidate their role in GC support, developmental stage and contributions to memory T cell pool.