Ultrastructural evidence of alveolar collapse was also present by the apposition of the alveolar septa ( Figure 2E -G). The regenerating bronchiolar epithelium extended along the adjacent alveolar septa showing features of cells with prominent surface microvilli with decreased or absent lamellar bodies and considerable cytologic atypia ( Figure 2H -L). Increased myofibroblasts and collagen fibers were also present ( Figure 2I ). Multinucleated epithelial cells with prominent nucleoli were noted in most cases, although such cells were sparse ( Figure 2K ). The proliferating bronchiolar and AECs containing TRS and CCC, probably representing residual viral-like particles, were distinguished in all cases ( Figure 2M -R). TRS appeared as reticular aggregates of branching membranous tubules located within the cisternae of the endoplasmic reticulum ( Figure 2M -O) or were compact ( Figure 2Q , R). CCC were identified as elongated, slightly curved cylindrical structures ( Figure 2P , Q), ring shaped ( Figure 2R ) or fused membranous lamellae, representing cisternae of endoplasmic reticulum. (Table 4) . Patients 3 and 5 presented with immunologic impairment.