O'Callaghan's left knee was tested on Wednesday and a call was made Thursday morning that he would not be fit to lock horns with the Azzurri.

Cullen will line up in the second row alongside Paul O'Connell, as he did against Fiji in November, for his first Six Nations game since staring against Wales in March 2003.

Despite accumulating just 20 caps including four Six Nations appearances for his country, the 32-year-old will not be fazed by the big stage having starred in Leinster’s Heineken Cup triumph last season.

Munster’s Donnacha Ryan is in line for his first Six Nations cap after replacing Cullen on the bench.

The selection is a mark of confidence in Ryan with boss Declan Kidney opting for the 27-year-old over experienced veteran Mick O’Driscoll.

Ireland Team & Replacements:

15 - Rob Kearney (UCD/Leinster)
14 - Tommy Bowe (Ospreys)
13 - Brian O'Driscoll (UCD/Leinster) (capt)
12 - Gordon D'Arcy (Lansdowne/Leinster)
11 - Andrew Trimble (Ballymena/Ulster)
10 - Ronan O'Gara (Cork Constitution/Munster)
9 - Tomas O'Leary (Dolphin/Munster)
1 - Cian Healy (Clontarf/Leinster)
2 - Jerry Flannery (Shannon/Munster)
3 - John Hayes (Bruff/Munster)
4 - Leo Cullen (Blackrock College/Leinster)
5 - Paul O'Connell (Young Munster/Munster)
6 - Kevin McLaughlin (St. Mary's College/Leinster)
7 - David Wallace (Garryowen/Munster)
8 - Jamie Heaslip (Naas/Leinster)

Replacements:
16 - Rory Best (Banbridge/Ulster)
17 - Tom Court (Malone/Ulster)
18 - Donnacha Ryan (Shannon/Munster)
19 - Sean O'Brien (Clontarf/Leinster)
20 - Eoin Reddan (Lansdowne/Leinster)
21 - Paddy Wallace (Ballymena/Ulster)
22 - Keith Earls (Young Munster/Munster)