Figure. Pneumocystis carinii (jirovecii), Source: Wikepedia (subject to the GNU Free Documentation License)
Regarding Pneumocystis pneumonia, which of the following is correct?

A. Sputum induction gives a diagnostic yield of <50%
B. Steroid is indicated if PaO2 <70mmHg or A-a gradient > 35 mmHg
C. Pneumocystis carinii (jirovecii) can be grown by special culture medium outside the infected host.
D. Severe pneumocystis pneumonia is characterized by lymphocytic lung inflammation that may result in diffuse alveolar damage.

Answer: B

Sputum induction gives a diagnostic yield of 50 to 90%.
The major obstacle to studying pneumocystis is the inability to achieve sustained propagation of the organism outside the host lung. Many investigators
have attempted to cultivate pneumocystis using a variety of techniques, but none have been successful.
Severe infection is characterized by neutrophilic lung inflammation.

Reference
Thomas CF Jr, Limper AH. Review Article: Pneumocystis Pneumonia. N Engl J Med 350:2487, June 10, 2004 (free full text)