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Table 2.

Dynamics of SI-Ep homing and colonization at steady state

 Input per 18ha (% of the respective IEL subset) Progenies of the18h-inpute (% of the respective IELs sub.) Resident IELs 
 Totalb Retained in situc Ratio naive versus cyclingd Totalf Ratio undivided versus dividedg Average life-span of IELs (days)h 
γδ ∼1.0 0.3 2:1 ∼3.3 1:15 38 (33–43) 
UncTCRαβ ∼2.0 0.4 1:1 ∼3.5 1:13 34 (26–39) 
CD8 ∼6.0 0.8 1:3 ∼8.0 1:12 19 (12–32) 
CD4 ∼25.0 3.6 1:2 ∼10.0 1:5 14 (12–16) 
 Input per 18ha (% of the respective IEL subset) Progenies of the18h-inpute (% of the respective IELs sub.) Resident IELs 
 Totalb Retained in situc Ratio naive versus cyclingd Totalf Ratio undivided versus dividedg Average life-span of IELs (days)h 
γδ ∼1.0 0.3 2:1 ∼3.3 1:15 38 (33–43) 
UncTCRαβ ∼2.0 0.4 1:1 ∼3.5 1:13 34 (26–39) 
CD8 ∼6.0 0.8 1:3 ∼8.0 1:12 19 (12–32) 
CD4 ∼25.0 3.6 1:2 ∼10.0 1:5 14 (12–16) 
a

At 18 h after transfer, the average frequency of donor CD3+ TDLs was ∼10% of CD3+ cells in peripheral lymphoid organs and blood, and ∼0.5% in the SI-Ep (Fig. 4 A). Assuming that the donor population was an unbiased representation of host circulating T cells, then the total number of cells (donor plus host) entering the SI-Ep during that period was ∼5% of IELs. This estimation is close to the frequency of CD69 cells (∼6%) in CD3+ IELs, a result that supports the above assumption.

b

In the 18-h SI-Ep immigrant pool, ∼11% were γδ+, ∼7% uncTCRαβ, ∼24% CD8+ and ∼53% CD4+ (Fig. 4 A). These values were referred to the 5% input per 18 h, and then to the average frequency of each T cell subset in IELs (Table 1).

c

The estimation of the frequency of immigrants retained in the SI-Ep was based on the frequency of donor cells that expressed CD69 at 44 h after transfer. For naïve immigrants (based on the analysis of RTEs), the percentage of CD69+ cells in each T cell subset were as follows: γδ+, 19.6%; uncTCRαβ, 13.3%; CD8+, 3.2%; CD4+, 4.9%. For cycling immigrants, >90% expressed CD69 in all T cell subsets. These values were then referred to the frequency of naive and cycling cells in the 18-h pool of immigrants, which were ∼90% and ∼10%, respectively, in all subsets (Fig. 4B).

d

These ratios were determined from the estimations of the number of naive and cycling immigrants retained in situ as described in c.

e

We designate as progenies of the 18-h input all donor immigrants that expressed CD69 by days 4 to 8 after transfer, regardless of whether they had proliferated or not.

f

The number of donor CD69+ cells in the SI-Ep was maximal by day 4 after transfer, and remained stable up to day 8 after transfer, except for γδ, whose maximal values were reached by days 6 to 8. The estimations were based on the analysis of 9 individually studied recipients.

g

Ratios between undivided cells and the progenies of cells that had proliferated, were estimated based on the CFSE profiles, of which representative examples are shown in Fig. 7, and take into account that only a fraction of the undivided cells expressed CD69, while this molecule was expressed by >90% of proliferating cells.

h

The average life span corresponds to values estimated in footnote f, to which the time period necessary to reach maximal values was added (about 7 d for γδ cells and 4 d for all the other subsets). Ranges are indicated in parenthesis.

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