Ulster hooker Best has only just returned to full-time training following a neck injury that had been expected to rule him out for the entire season.
Like Best, Horan missed out on Ireland's autumn internationals against Australia, Fiji and South Africa after undergoing a routine medical procedure for a minor heart ailment.
The loosehead prop finally featured for Munster against Northampton on Friday night having spent three frustrating months on the sidelines.
Wallace has been struggling with an ankle injury in recent weeks but he did play an important role in Ulster's impressive European win at Bath last weekend.
His inclusion in the A squad just a week before the start of the Six Nations has led critics to suggest that Leinster's Gordon D'Arcy could be given the No12 shirt when Ireland host Italy in their tournament opener.
That is not the official line coming out of the Ireland camp itself, however, with the IRFU team announcement stating, "The selected squad includes several players who have recently made their returns from injury or who will be looking to increase their competitive game-time ahead of the start of the 2010 RBS 6 Nations Championship."
Munster have seven players named in the matchday 22, while Ulster and Leinster both have six, Connacht have two and Leicester Tigers have one.
One of those Munster players, Denis Hurley, is being closely monitored as he recovers from a leg injury which saw him pull out of Munster's last competitive fixture. A final decision on Hurley's fitness will be made later in the week.
Ireland A squad vs England Saxons, The Recreation Ground, Sunday January 31, kick-off 2pm
Rory Best (Ulster)
Isaac Boss (Ulster)
Tony Buckley (Munster)
Ryan Caldwell (Ulster)
Darren Cave (Ulster)
Ian Dowling (Munster)
John Fogarty (Leinster)
Marcus Horan (Munster)
Ian Humphreys (Ulster)
Denis Hurley (Munster)
Shane Jennings (Leinster)
Keith Matthews (Connacht)
John Muldoon (Connacht)
Fergus McFadden (Leinster)
Johne Murphy (Leicester Tigers)
Mick O'Driscoll (Munster)
Sean O'Brien (Leinster)
Niall Ronan (Shannon/Munster)
Mike Ross (Leinster)
Peter Stringer (Munster)
Devin Toner (Leinster)
Paddy Wallace (Ulster)
Guinness PRO12
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