Still working on whether this is SP-A (surfactant protein A) in the layered protein paracrystalline type banding seen in the RER of at least three species of mammal. The most prominent of these banded protein products in the RER of alveolar type II cells seems to have occurred in guinea pigs, though they were first observed in ferrets.  These six images are high mag images where just the RER with the layered protein are highlighted (with the black arrow). Since they all came from different images and magnification is just to messy to calculate I have substituted the 20 nm ribosome as a “scale”  so the red dots are a “relative” measurement of 20 nm.  This puts all the intracisternal bodies in perspective.

The dog is different than the other two species in which the intracisternal body in RER of type II alveolar cells is seen as I have only found them with a single banding period…. whereas in guinea pigs the number of periods in a single RER profile with this protein can be very large and difficult to count because of the perpendicular and arched and oft changing directions of the layering.  However, the mean number of bands in guinea pigs, 787 periods,  n=189 RER profiles,  produced a mean of 4.1 (SD=2.9) +- 0.21 (SEM) periods per profile while in ferret of the 625 periods counted, n=123 profiles of RER, the mean number of periods per profile of RER was 2.66  (SD=4.9) +- 0.39.  Mongrel dog had very few profiles, and number of profiles was = to the number of periods (n=7).  Six of those are shown in the figure below:  they were about 100 nm thick and maybe twice that long.

Adding some SP-A profiles (?) and ribosomes from a second tangential section through an intracisternal body.  I am more and more convinced that the major dark band seen in these profiles within the RER of some type II alveolar cells (many of which are posted in this blog) when sectioned tangentially show the bouquet of the 18-mer of SP-A splayed out giving a hexagonal- or oval-like structure.  These are not plentiful, but also not infrequent, and are just prominent enough to be given attention.  As a comparison, I have examined immediately adjacent cytoplasm and do not see this kind of arrangement of the cytoplasm, therefore it seems NOT to be an random artifact of fixation (though we all recognize that fixation induces artifact of necessity) the hexagonal patterns are found in tangentially sectioned areas of the intracisternal bodies.

This is an interesting picture. It derives from a micrograph from an untreated ferret (my animal # 2, negative 4640, block 18578, 27,900 x magnified 4 x) and scanned and processed in photoshop  using contrast, color balance, dodge and burn only.  While continuing to look for molecules that might be surfactant protein A, the round to hexagonal objects with a central density appeared sometimes to be closely linked with ribosomes at the edge of the RER membrane when the occasional opportune tangential section of an intracisternal body in a type II cell is achieved.

These round SP-A? molecules are more prominent in guinea pig micrographs, but this array along the growing edge of a profile of RER was particularly nice in that several adjacent ribosomes were adjacent to several round-to hexagonal profiles of what might be protein product.

I have highlighted the ribosomes and round structures in blue, put a red arrow pointing the a ribosome, a light red line around one such round to hexagonal structure (left in the figure below) and also shown a blue box around the original cisternal body and ribosomes (photoshopped only with contrast and brightness) (right in the figure below.  The relative sizes: ribosomes, approx 20 nm, the hexagonal structures about twice that.

Most publications give the SP-A molecule as being around 25 microns…. i think if the “bundle of flowers” typically assigned to SP-A 18-mer were to spread out at the head… that the dimension when seen from the top could closely approximate the dimension found here.  Each ribosome can be used as a guide to magnification.