class MyClass
{
    public Queue variable;
    internal MyClass()
    {
        variable = new Queue<int>();
        variable.Enqueue(1);
        Thread thread = new Thread(new ThreadStart(DoSomething));
        thread.IsBackground = true;
        thread.Start();
    }
    public void DoSomething()
    {
        int i = variable.Dequeue();
        MessageBox.Show(i);
    }
}

class MyClass {
    public Queue variable;
    internal MyClass() {
        variable = new Queue();
        variable.Enqueue(1);
        Thread thread = new Thread(new ThreadStart(DoSomething));
        thread.IsBackground = true;
        thread.Start();
    }
    public void DoSomething() {
        int i = (int)(variable.Dequeue()); //cast required here
        //MessageBox may not play nice from non-ui thread
        Console.WriteLine(i);
    }
}

public Queue<int> variable;

MessageBox.Show(i.ToString());