Probiotics are essential for human physiological health. You will want to supplement with many different types. One key type is Lactobacillus acidophilus (L. acidophilus).
You will find several different types of Lactobacillus in probiotics. L acidophilus has the following helpful effects on human physiology according to the research.
Increases naïve T cell interferon (IFN) secretion
Supports Th1 immune activation
Increases IFN, IL-6, TNF-alpha
Stimulates innate immune system to protect against pathogens
You might notice that some of these functions are different than what we see with other Lactobacillus like reuteri and casei. Most probably, you need all of these all the time in healthy intestinal colonies to maintain the necessary balance. If you happen to be a Th2 dominant type person you might want to supplement more with L. acidophilus than L. reuteri or L. casei. But as was stated, most will want to take all of these strains and let your body's innate intelligence sort it out.