Traditional assays for anti-PCNA are double immunodiffusion and HEp-2 IFA. Positive anti-PCNA antibodies as defined by these assays are probably high titer and are associated with SLE. The “new” assays for anti-PCNA using ELISA, Line/Dot blot, CLIA, FEIA, ALBIA, and other solid-phase methods typically detect lower titer (or lower avidity) positives (e.g., higher sensitivity than IFA and immunodiffusion) and this may explain why studies using these methods no longer show a specific association of anti-PCNA with SLE (Vermeersch et al, 2009). More studies are needed on this topic.

A second consideration with anti-PCNA antibodies is that their reactivity has been reported to be highly dependent on the oxidation status of PCNA in the HEp-2 substrate (Tsai et al, 1992). The initial fascinating observation was that if the HEp-2 slide is taken out from the nitrogen-sealed packet at room temperature for 15-30 minutes before starting the first incubation of the diluted serum in the typical IFA protocol, the anti-PCNA staining was negative or substantially reduced while other ANA were not apparently affected. This loss of reactivity to PCNA was apparently due to air oxidation. The report showed that the free thiol group(s) on PCNA is important for anti-PCNA reactivity of samples from SLE patients. Thus, back to the question, the “negative (result) in HEp-2 IFA” would have to be considered more carefully by processing the slide immediately after opening the sealed packet, by using at least one additional HEp-2 slide brand, and by confirming the expected HEp-2 IFA AC-13 pattern with an available reference anti-PCNA serum.

Please note that there have not been any known recent reports that reproduced the data on the oxidation status-dependency of anti-PCNA staining as reported by Tsai et al. ~30 years ago. This is important because HEp-2 substrate processing, stabilization and fixation may have changed since then. In summary, anti-PCNA reactivity in a solid phase assay accompanied by the typical AC-13 pattern may be more specific for SLE compared to a positive reaction in solid phase assays alone.

References
Vermeersch P, De Beeck KO, Lauwerys BR, Van den Bergh K, Develter M, Marien G, Houssiau FA, Bossuyt X (2009) Antinuclear antibodies directed against proliferating cell nuclear antigen are not specifically associated with systemic lupus erythematosus. Ann Rheum Dis 68:1791-1793. DOI: 10.1136/ard.2008.104190

Tsai WM, Roos G, Hugli TE, Tan EM (1992) Influence of free thiol group(s) on autoantibody-defined epitope of proliferating cell nuclear antigen. J Immunol 149:2227-2233.

Mahler M, Miyachi K, Peebles C, Fritzler MJ. The clinical significance of autoantibodies to the proliferating cell nuclear antigen (PCNA). Autoimmun Rev. 2012 Aug;11(10):771-5.

Mahler M, Silverman ED, Fritzler MJ. Novel diagnostic and clinical aspects of anti-PCNA antibodies detected by novel detection methods. Lupus. 2010 Nov;19(13):1527-33.

The term "nuclear speckled" is an overarching competent- HEp-2 IFA pattern that includes both fine speckled (AC-4) and large/coarse speckled (AC-5). In some cases, it can be difficult to define precisely the speckled pattern a sample produces, being either the fine or large/coarse speckled pattern. Obviously, one may use the ICAP competent level terminology AC-4/5. In such case, one may combine the antibody targets and clinical relevance of the individual patterns, i.e., AC-4 and AC-5. Using the competent level AC-4/5 term may also be appropriate in mixed patterns caused by more than one autoantibody specificity in the sample.
Ideally, one should provide the most complete definition of the pattern (expert level), because these provide more specific information on antigenic associations and clinical relevance. For example, as indicated in the "antigen association section" of ICAP website, the nuclear coarse speckled pattern (AC-5) is associated mainly with anti-Sm and anti-U1-RNP antibodies, whereas the nuclear fine speckled pattern (AC-4) has a broader target antigen association. In the ICAP Note #2, AC-4 can be further divided into fine speckled with myriad discrete tiny dots (AC-4a), or simple fine speckled (AC-4b). These are defined patterns and have respective antibody targets, immunological associations, and clinical relevance. The nuclear dense fine speckled pattern (AC-2), on the other hand, should be distinguished from the nuclear speckled patterns AC-4 and AC-5 based on the positive staining of the metaphase plate. With exception of the centromeric pattern (AC-3), the clinical relevance of all patterns is only indicated if the antibody target has been identified.