Type 2 dendritic cells (DC2) are a heterogeneous DC population, responsible for driving T helper cell responses. In murine spleen, two major DC2 subpopulations can be distinguished by mutually exclusive expression of ESAM and CX3CR1. ESAM⁺ DC2 were shown to differentiate from two ontogenetically distinct cell types, SiglecH^– conventional (c)DC2 precursors (pre-cDC2) and SiglecH⁺ CX3CR1⁺ transitional DCs (tDCs) which exhibit features of both plasmacytoid DCs (pDCs) and DC2. tDCs differentiate into ESAM+ DC2 (called tDC2) but also contribute themselves to the inflammatory response to viral infection. Similar to pDCs, tDCs and tDC2 show a high degree of labeling in hCD2-Cre;R26-lsl-tdTomato mice indicating their common origin from a progenitor with lymphoid features.

By employing high-dimensional flow cytometry we explored DC population kinetics and activation during acute LCMV Armstrong infection in hCD2-Cre;Rosa26-lsl-tdTom mice. All splenic DC2 subsets were found reduced in numbers on days 3 and 5, followed by recovery on day 10 after infection. Splenic pre-cDC2s and tDCs were both reduced on day 3 and partially replenished on day 5. While tDC number recovered on day 10, pre-cDC2 were still reduced.

The frequency of hCD2-traced cells within the ESAM⁺ DC2 subset remained stable on days 1, 3, and 5 and increased slightly on day 10 after infection in line with a faster recovery of the tDCs. tDCs responded to the infection with transient upregulation of CD86 on day 1. ESAM⁺ and CX3CR1⁺ DC2 differed in the magnitude and kinetic of CD86 and CD64 upregulation, whereas differences between the hCD2-traced and -untraced fractions within ESAM⁺ DC2 were less pronounced.

In summary, we show that in response to LCMV Armstrong infection, both tDCs and pre-cDC2 contribute to DC2s, with tDC numbers recovering faster. Functional heterogeneity of DC2 is associated more with their subtype and less with their origin.